In the previous version of firmwares it was a kind of pain to downgrade to any previous firmwares which makes it so difficult to you.. But in beta versions it is so easy to downgrade as Apple is still actively signing iOS 5.1.1 due to the fact that it’s the latest public firmware available. So here’s how to downgrade:
STEP 1: Enter your iPhone in DFU Mode.
STEP 2: Then open iTunes and downgrade.
How To Downgrade iOS 6 To iOS 5.1.1 [ Video ] :