How to Downgrade Windows Phone Preview For Developers to normal

What you'll need

• A Lumia
• Nokia Recovery Software Tool

Link for download the Nokia Recovery Software Tool

• Click here to download

PC requirements to use this recovery tool

• Microsoft Windows 7 or later.
• USB cable to connect your phone to the computer.
• Minimum 2 GB free storage space.
• The files downloaded by the Nokia Software Recovery Tool may be as much as 4GB, and may take a long time, depending on your internet connection and phone model.

Does this work with my Windows Phone from HTC, Samsung or another phone maker?

No. This software is just for Lumia handsets from Nokia.

Steps

• Download and install Nokia Recovery Software Tool
• Open Nokia Software Recovery Tool
• Connect your Lumia to the PC with a USB cable
• You'll see which software version you can install on your Lumia – Click install below that
• You will need to acknowledge that the data and content on your phone will be erased. If you can still access your phone, make a backup by going into settings -> backup . You'll also need to know that photos, music and apps will be wiped during this reset process. Click that you understand and then click continue.
• You'll now begin downloading the software. Network speeds vary, 

• The software will now begin installing to your phone. Do not use your phone or disconnect the cable during this step. Just go for a quick walk while your phone and PC do their thing.

• You're done.

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End of support for Windows Phone 7.8 & 8

Microsoft will end the support of Windows Phone 8 on July 8 2014, for Windows Phone 7.8 October 9 2014 is last day for support.

Products Released	Lifecycle Start Date	Mainstream Support End Date	Notes
Windows Phone 7.8	February 9 2013	October 9 2014	Microsoft will make updates available for the Operating System on your phone, including security updates, for a period of 18 months after the lifecycle start date. Distribution of the updates may be controlled by the mobile operator or the phone manufacturer from which you purchased your phone. Update availability will also vary by country, region, and hardware capabilities.
Windows Phone 8	December 14 2012	July 8 2014	Microsoft will make updates available for the Operating System on your phone, including security updates, for a period of 18 months after the lifecycle start date. Distribution of the updates may be controlled by the mobile operator or the phone manufacturer from which you purchased your phone. Update availability will also vary by country, region, and hardware capabilities.

After end of support Windows Phone 7.8 & Windows Phone 8 Microsoft will not provide any update/solution for it.

Windows Phone 7 update history

Update 7.10.8862.144

Also known as Windows Phone 7.8*.

Start. Provides resizable small, medium and large Live Tiles so you can customise your Start experience in new ways.
Accent colours. Expands the number of available accent colours to 20.
Lock screen. Improves the lock screen experience with accidental wipe protection features and the Bing image of the day wallpaper.
Marketplace and Xbox. Expands Windows Phone Marketplace and Xbox support to new countries and regions.
Fonts. Enhances the Chinese font and improves the appearance of Arabic and other languages.
Live Tiles. Fixes performance issues from a previous update.
Other improvements. Includes many other improvements to Windows Phone.
This update is not available in all markets or for all phones.

*Windows Phone 7.8 is the official product name Microsoft use to describe this release. However, due to a quirk of software development, the actual OS version is identified as 7.10.8862.144. You'll see both of these names on your phone in Settings  > About > More information.

Update 7.10.8773.98

Messaging. Adds new messaging capabilities to your phone. You can now attach multiple pictures, videos, audio notes and ringtones to text messages.
Other quality improvements. Includes many other improvements to Windows Phone.
This update is not available in all markets or for all phones.

Update 7.10.8107.79

On-screen keyboard. Fixes an issue to prevent the keyboard from disappearing during typing.
Email. Fixes a Gmail synchronisation issue.
Location. Fixes a location access issue. With this fix, the Me feature in the People Hub only sends anonymous information about nearby WiFi access points and mobile phone masts to Microsoft if you agree to allow the Check In function to access and use location information.
Security. Revokes digital certificates from DigiCert Sdn Bhd to address an encryption issue.
Email threads. Fixes an email issue related to Microsoft Exchange Server 2003. With this fix, when you reply to or forward a message, the original message is now included in your response.
Voicemail. Fixes a voicemail notification display issue that occurs on some European and Asian networks under certain conditions.

Update 7.10.7740.16

Email threads. Fixes an email issue related to Microsoft Exchange Server 2003. With this fix, when you reply to or forward a message, the original message is now included in your response.
Voicemail. Fixes a voicemail notification display issue that occurs on some European and Asian networks under certain conditions.
This update is available only in certain markets.

Update 7.10.7720.68
Also known as Windows Phone 7.5*.

Hundreds of new and improved features. Based on your feedback, Microsoft have scoured Windows Phone from top to bottom looking for ways to make it easier for you to connect and share with friends, discover and use smarter applications, and tap into the power of the web.
*Windows Phone 7.5 is the official product name Microsoft use to describe this release. However, due to a quirk of software development, the actual OS version is identified as 7.10.7720. You'll see both of these names on your phone in Settings  > About > More information.

Update 7.0.7392.0

Fix for fraudulent third-party digital certificates. This update includes a critical fix to an industry-wide issue with nine untrusted digital certificates that were issued by one root certificate authority. These third-party digital certificates are used to access popular websites and email portals.
Although this is not a Microsoft security vulnerability, these untrusted certificates may be used to spoof content, perform phishing attacks or perform man-in-the-middle attacks against all web browser users. This update moves the affected certificates to the "Untrusted Publishers" certificate store on Windows Phone, which helps ensure that these fraudulent certificates are not inadvertently used. For more info, see Microsoft Security Advisory (2524375).

Update 7.0.7390.0*

Also known as the "NoDo" update.
Copying & pasting. Press a word and drag the arrows to copy and paste text on your phone. You can copy text from emails, text messages, web pages and Office Mobile documents, and paste it anywhere you can type. To learn more, see Copying and pasting.
Faster applications and games. Nobody likes to wait. That's why Microsoft've whittled down the time it takes for applications and games to start up and resume. It's all part of our focus on getting you to the things you love, easier and faster.
Better Marketplace search. Microsoft have streamlined Marketplace search to make it easier to find specific applications, games or music. Press the Search button in the Applications or Games section of Marketplace and you'll only see applications or games in the results. Press Search in the Music section of Marketplace to search just the music catalogue.
Other Marketplace improvements. Microsoft have improved the stability of Marketplace while you download applications. Microsoft have also improved the experience of downloading applications that are larger than 20 megabytes, upgrading from trial applications to paid applications, sharing links to applications via email, sorting Xbox LIVE games by release date and creating an Xbox LIVE account from within the Games Hub.
WiFi improvements. Microsoft have now display your phone's Media Access Control (MAC) address in Settings. (You might need this info if you try to connect to a WiFi network that uses MAC address filtering. To learn more, see Connecting to a WiFi network.) Microsoft have also removed the limit on the number of WiFi profiles that you can store and reduced the time it takes to start your phone if you've stored lots of WiFi profiles.
Outlook improvements. Microsoft have improved the experience of viewing iPhone photo attachments you receive from a non-Exchange-based email account (such as a Gmail, Hotmail or Yahoo! Mail account), using the Global Address List (GAL) when connecting to Exchange Server 2003 using Exchange ActiveSync, and working with email display names that contain brackets (for example, "David Alexander [Contoso]").
Facebook integration. Microsoft have improved the experience of synchronising Facebook accounts.
Camera improvements. Microsoft have improved the stability of switching between camera and video modes.
Audio improvements. Microsoft have improved the experience of using a Bluetooth headset to make calls when you're playing music or videos.
Other performance improvements. This update also includes software from several phone manufacturers that improves the performance of specific models. Naturally, if you don't have one of the affected models, Microsoft won't install this portion of the update on your phone.
*New phones with OS version 7.0.7389.0 include all of the features and improvements that are included in OS version 7.0.7390.0.

Update 7.0.7008.0

Update process improvements. This behind-the-scenes update improves the update process itself.

Windows Phone 8 update history

Update 8.0.10211.204

Messaging improvements. A great messaging experience is now even better. You can now add multiple recipients at the same time when you send a text message and automatically save unsent text messages as drafts. You can even edit received text messages before you forward them.

Text replies to incoming calls. Can't take a call? Now you can send a prewritten text reply to a caller directly from the call answer screen. It's a nice way to let people know that you're not ignoring them.

Internet Explorer improvements. You can now change your settings to prevent pictures from downloading automatically – an easy way to help keep data usage low. You can also delete selected sites from your browsing history and leave the rest intact.

WiFi connectivity. Have a favourite WiFi network? Windows Phone 8 will now prioritise WiFi connections based on your connection history.

Other improvements. Includes many other improvements to Windows Phone.

This update will be made available at different times, depending on your country or region, mobile operator and phone model.

How to update 7.8

What is needed to install 7.8 in your 7.5 phone

You should have an computer
You should have datacable of your phone
You should have windows XP SP3 or Vista or 7 or 8 installed in your computer
If you have Windows 8 in your computer then you need to install .net 3.5
Zune should be installed in your computer, if you don't have Zune installed in your computer then you can download it from http://go.microsoft.com/?linkid=9753463
It will be much better if you will install update from Primary computer
If you are updating your phone from primary computer then you have no deed to worry about you data (like: Images, videos, songs, contacts, messages, installed applications and all settings) all data will be safe,

Important note:
if you are updating your phone from laptop than make sure that your laptop's battery has sufficient power for update your phone
you should not use your phone when you're updating it
You should not disconnect your phone when phone is updating

How to install
Step 1 attach your Windows Phone 7.5 with your computer via datacable, and make sure that phone screen is not locked, If locked then unlock it, Zune will automatic start, if zune not start then start in manually.

Step 2 Click on Phone

Step 3 Click on Settings

Step 4 Click on update

It will take some time to check for updates,

Step 5 after check it will show that update found and it will display list of features of new update.

Step 6 Click on update now button
Step 7 it will start updating your phone

It will take approximately 10 minutes for update your phone, Note: time may be vary, time depend on your internet connection speed, computer performance, and size of data which stored in your phone.
You phone will restart several times and some time phone screen will show like this

Step 8 in last it will check for additional updates

Step 9 Now phone is updated, you can now disconnected phone from computer and can use it.

Note: After update 7.8 you may feel that your phone is working very slow, but it will be all right after 1 hour.

Problems:
When you check for update and it show error like following image then it means that you have not installed Zune in proper way, you need to reinstall Zune

If it shows no update available and if you have purchased your phone with any contract then make sure that 7.8 is available for your device right now or not, You should contact with your cellular service provider.

If it show no update available, but 7.8 update is available in your country for your mobile then in computer open CONTROL PANEL, here you will find REGION option.

Open it, here click on Location option and select your country,

then click on ok button and check for update again.
If 7.8 is not available in your country and your phone is unlocked (here unlocked mean that you can use any GSM sim in your phone) then open Control Panel and open region, here in location tab select that country where 7.8 is available, for example you can choose India  because in India 7.8 is released. now press ok button and try for update your phone :)
If it not work there here is another way to update your Windows Phone 7.5 which I've explained here