Do you miss Google Maps? Did the iOS 6.0 update shorten battery life on your A4 device? Whether you upgraded by mistake, or you're just looking to bring back the older firmware, now you can downgrade your iPhone 4 or iPhone 3GS to iOS 5.1.1. The following iOS downgrade instructions work on most A4 devices, including the iPod touch 4G.
Now that Apple has stopped signing older firmware, you must have your SHSH blobs saved for iOS 5.1.1 for this procedure to work properly. Downgrading will also require that you have the appropriate IPSW firmware file downloaded to your computer. You can grab iOS 5.1.1 for the iPhone 4 here, or for the iPhone 3GS at this link. Make sure you know where this IPSW file is saved before starting the instructions below.
1. Download redsn0w 0.9.14b2 from iPhone Dev-Team.
2. If your SHSH blob is stored on your computer, put it in the same folder as the iOS 5.1.1 IPSW file. If your SHSH blob is stored on Cydia, then proceed to step 3.3. Put the iPhone you are downgrading from iOS 6 to iOS 5.1.1 into DFU mode.
4. Open redsn0w and navigate to Extras -> SHSH blobs -> Stitch.
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5. Select IPSW and choose the iOS 5.1.1 IPSW file for your iPhone.
6. If your SHSH blobs are stored on the computer, select Local and choose the iOS 5.1.1 SHSH file. If your SHSH blobs are stored on Cydia, select Cydia.
7. After your SHSH blob and IPSW firmware files are located redsn0w will proceed to stitch them together. This makes it possible for the new custom firmware to be installed without Apple signing iOS 5.1.1 for your device.
8. When redsn0w is finished stitching, go back twice and select Pwned DFU.
9. Open iTunes on your computer. The iPhone should appear as a device in recovery mode. While holding down the Option key on the keyboard, click the Restore button. Choose the stitched custom firmware file redsn0w just created.
10. Wait for iTunes to restore your iPhone. An unknown error (-1) dialog box might appear.
11. Go back to redsn0w and navigate to Extras -> Recovery fix. Put your iPhone into DFU mode again.
12. Once redsn0w finishes with the recovery fix, your iPhone will be successfully downgraded to iOS 5.1.1.