In order to continue you will need to have SHSH Blobs saved for the lower firmware version you are downgrading to. You can use RedSn0w or TinyUmbrella to save your SHSH blobs. Also make sure you have performed a backup of your device using iTunes.
You may want to do this to downgrade from iOS 5.1.x to iOS 5.0.1 for jailbreak.
Create a folder called Pwnage on your desktop and download the following items into the folder.
- The latest version of RedSn0w
- The current iOS firmware (iOS 5.1.1)
- The older firmware you want to downgrade to (iOS 5.0.1)
Extract the RedSn0w archive.
Launch the RedSn0w application from the extracted RedSn0w folder by right clicking its icon and select Run as Administrator from the contextual menu.
Select Extras from the main menu.
Choose Even More from the extras menu.
Select Restore from the even more menu.
Click the IPSW button.
Navigate to the Pwnage folder on your desktop and choose the firmware ipsw you would like to restore to and click Open.
You will be informed that an additional IPSW is required. Make note of the ipsw file requested and click the OK button.
Select the additional ipsw specified in the previous step and click the Open button. (This will likely be the most current firmware ipsw).
You will be warned that if you continue your baseband will be updated to the latest version. If you want the best chances of unlocking your phone in the future you should not continue. If you do not care about an unlock click the YES button.
You will now be informed that your device will be placed into recovery mode. Click the OK button.
You must now select your blobs for restore. You can choose to specify local blobs or remote blobs.
- Choose this option if you previously saved your blobs with RedSn0w and they were stored on the Cydia server. This is the easiest option if it's available to you.
- Choose this option if you previously saved your blobs with TinyUmbrella or you used RedSn0w but did not let Cydia save a copy of your blobs.
- After clicking Local you will be prompted to select your saved blob file for the firmware you are downgrading to. If you used TinyUmbrella, simply navigate to your home folder and go into the .shsh folder with your saved SHSH blobs. Select the file that matches the ECID displayed in RedSn0w and the firmware version you are downgrading to, then click Open.
RedSn0w will now stitch your blobs to the firmware ipsw and automatically begin a restore to the modified firmware.
You will be informed that your restore has been successful! If you were downgrading to jailbreak you can find jailbreak instructions here.