How to Downgrade your iOS in iPhone 4S, iPad 2 and the new ipad to iOS 5.0.1 using Redsn0w
Step 1: If you haven’t yet, download the new Redsnow
Step 2: If you haven’t yet, upgrade to iOS 5.1.1.
Step 3: Turn your device in DFU mode and run Redsn0w.
Step 4: After RedSn0w detects your device in DFU mode, goto Extras > Even more > Restore and click IPSW under the IPSW section. RedSn0w will then ask you for your iOS 5.0.1 IPSW. Once you locate iOS 5.0.1, RedSn0w will ask your for the latest firmware (iOS 5.1.1).
Step 6: After your blob is verified, your work is pretty much done, Just wait till redsn0w finishes the downgrading.
Step 7: After a success message appears, go to Settings > General > About and see you firmware now degraded.
After that you can use our guide here on how to jailbreak your device.