Here we are going to learn on how to downgrade from iOS 6 beta 1 to iOS 5.1.1 firmware. Once you have managed to downgrade back to the older firmware you can continue to untethered jailbreak your iOS device.
Anyway let's downgrade our iOS 6 beta 1 to the older version right now, please proceed at your own risk.
How To Downgrade iOS 6 Beta 1 To iOS 5.1.1
Download iOS 5.1.1 for you iDevice
Step 1. Connect your iPhoen to computer using USB and then open iTunes.
Step 2. Put your device into DFU mode. Follow the following guide.
DFU mode: Hold the Home and Power button together for about 10 seconds, afterward release the Power button while still holding the Home button, wait till you see a popup message appears from iTunes saying that it has detected your device in recovery mode.
Step 3. Now choose your device model from iTune's sidebar, then hold down -- Alt for Mac and Shift for Windows -- then click Restore button. Now point the device to iOS 5.1.1 ipsw file. The process takes about 10 or 15 minutes at maximum. Once it's done, you are back to iOS 5.1.1. Congrat!
That is how to downgrade iOS 6 beta 1 to iOS 5.1.1 and hope you find this post useful.