How to Downgrade from iOS5 to 4.3.5 or 4.2.10
Recently, Apple has been cracking down on unauthorized iOS5 users. It has been determined that Apple has identified several developer accounts who broke their TOS by selling their UDID slots for a fee to iDevice users who wanted to try out the iOS5 beta firmware. Apple has begun shutting these developer accounts and if you are one of the people who purchased a UDID slot you will now notice that your device is nothing more than a paper weight.
Please follow the instructions below(Mac/Win) to downgrade from whatever iOS5 beta you are on back to 4.3.5 or 4.2.10(CDMA).
Step 2: Connect your device that is running iOS5 to your computer and turn it off.
Step 3: Put your device into DFU mode by holding down home and power for 10 seconds and then releasing power but continue holding home for another 10 seconds. If you have troubles, check out our DFU mode video tutorial.
Step 4: iTunes should detect a device in recovery mode and your screen should be black.
Step 5: Hold down shift(win) or option(mac) and press the "restore" button. Select the 4.3.5 or 4.2.10 firmware file you downloaded in step 1 and the downgrade will initiate. Once it is done, your phone will reboot and you will be back on 4.x firmware.