How to downgrade from iOS 6 to iOS 5.1.1?
Solution 1:
In general, you will need to jailbreak (if that's even possible on the new iOS) the device to revert the OS. iOS upgrades (OTA or via iTunes) are one way and have been that way (unable to downgrade) since the 1.0.
Hopefully someone will see your plea for help once they know if and how a jailbreak will work. In the past you needed to get shsh keys from Apple and there was a limited window after updates to get the old keys. If this is so, time is of the essence for you. I haven't been keeping up on jailbreaking enough to even recommend a wiki or reputable source other than to recommend you search the internet.
Of course if someone hasn't already asked a how to jailbreak iOS 6 question here, you are free to ask that question as well or edit that into this question.
Solution 2:
I just read this blog post and it looks like it's possible to downgrade but only if you do it quickly. Soon there will be no turning back.
Also, it's device dependent, as explained in this post
It worked for me to restore an old back up.
Solution 3:
You will need the following programs:
- iTunes latest version
- iREB
- Tiny Umbrella
First open up iREB, select your device and put it into DFU mode. Once it is done you will get a message stating that your device is now in DFU mode.
Second you then need to open up Tiny Umbrella and click "Start the TSS server."
Third, open up iTunes. A message will pop up reminding you that your device is in DFU mode. Hold down Shift when you click the restore button and choose the firmware. It may take a while to load the firmware but it does work.
This process also works for custom firmware as well.