Nokia Lumia 1520 is now receiving the official Windows Phone 8.1 update from AT&T but users who have the Preview for Developers installed on the smartphone can't get the upgrade. Here are the steps in order to downgrade Lumia 1520 to get Windows Phone 8.1.
Downgrading Lumia 1520
According to WPCentral, users who own any Nokia Lumia 1520 running the Preview for Developers are unable to receive the Nokia Lumia Cyan Update containing Windows Phone 8.1 software.
Based on the information, it seems like that the problem originated on the BitLocker encryption provided by the Preview for Developers if enabled. If Windows Phone 8.1 is installed on this scenario, the smartphone will initiate a "lock-up" preventing the software upgrade as part of its security measure.
"We are currently investigating the issue. We have paused delivery of the update to customers using the Preview for Developers and will resume once a fix is in place. Customers whose phones have been affected should use the Nokia Software Recovery Tool to return your Lumia to a normal commercial software state before downloading the Lumia Cyan update," Microsoft's official statement to WPCentral.
Users of the Lumia 1520 with Preview for Developers will need to downgrade the smartphone to run the Lumia Cyan Update normally.
Downgrading the Device
Microsoft strong advises to downgrade the Lumia 1520 to Windows Phone 8.0 to receive the Lumia Cyan Update without having any trouble during installation.
1. Create a backup of all data files, personal settings and other configuration stored on the smartphone. Go to Settings > Backup > App + Setting > Backup now. Manually backup multimedia files such as photos and videos.
2. Download the Nokia Recovery Software Tool on the computer to downgrade the Lumia 1520 to Windows Phone 8.0.
3. Install the Nokia Recovery Software Tool on the computer running Windows 7 or higher.
4. Launch the Nokia Recovery Software Tool on the computer.
5. Connect the Nokia Lumia 1520 to the computer using a USB cable.
6. A message will appear displaying the software options for Lumia 1520. Select Windows Phone 8 then click install below that.
7. Another prompt will appear regarding the user's acknowledgement on the deletion of data and contents stored on the smartphone. If it's possible to access the device, create a backup now. The software installation will wipe out everything, so make sure it is good to go before proceeding.
8. Installation may take up to 15 minutes or longer depending on the speed of the Internet connection.
9. Once the installation process begins, do not interrupt it, use the smartphone, unplug the USB cable or turn off the computer.
10. After the installation, users can now start downloading Windows Phone 8.1 official update.