Following on from the release of the Windows Phone 8.1 Developer Preview one month ago, Brandon LeBlanc from the Windows Phone Blog has let us know that there is now an update available for those of you who have installed the Windows Phone 8.1 Developer Preview on your devices.
The update mainly focuses on bug fixes and improving battery life. However, I noticed it does add the FM Radio app as FM Radio is now not included in the Music app.
Check out his article for more details:
Just go to Settings >> Phone Update and click "Check for updates".