AFAIK, when Apple stopped signing their firmware, this made it difficult if not impossible.
I am currently using Iphone 4S on IOS 9 but after upgrading to IOS 9 I am facing many problems.
Sometimes phone just hangs, sometimes I can't swipe between screens. I think my phone's hardware can't support software optimally. Is there any method to downgrade from IOS 9 to IOS 7 ??
Please help me. Currently my phone is non-jail broken but I can jailbreak if required to do so.
Any help in this regard would be much appreciated.