Go to iMZDL: iOS 5 & Mac OS X 10.7 and find the iOS 5 GM that fits you (CDMA iPhone 4).
Plug your device in and open iTunes. Go to your device, right click on it and back it up. Then when the back up is finished, hold shift and click restore (Back Up BEFORE doing this).
A window will pop up asking you to choose a file, and you will choose the CDMA Phone 4 .ipsw file that you download from iModZone. It will tell you your device will be restored to iOS 5, agree, go through the process, then after the restore choose the latest backup. Back it up, and there you are - you're running the final release of iOS 5.