How to downgrade to official Windows Phone firmware?

Customers whose phones have been entitled to receive a particular update but have not received because of developer preview should use the Nokia Software Recovery Tool to return your Lumia to a normal commercial software state.

Here is what you need to downgrade to official windows phone firmware.

Windows Device Recovery Tool (download link)
Microsoft Windows 7 or newer.
USB cable to connect your phone to the computer.
Minimum 4 GB free storage space.

Steps:

Start the tool on computer and connect your phone via a USB cable when asked to.

The tool will now download the latest software for your device. The download time will depend on the size of the software and your network speed. When the download is finished, the tool will prompt you to install the software along with a ‘Full Wipe‘ warning.

How to downgrade to official Windows Phone firmware?

Hit ‘Install‘ . Now sit back and relax, the tool will now perform a full wipe and a re-install of the latest OS on your windows phone device. Once the installation is finished, you phone will be rebooted.