Downgrade From iOS 5 to iOS 4.3.3, iOS 4.3.2, iOS 4.3.1, iOS 4.2.1 or iOS 4.1
iOS 5 has recently be released by Apple in WWDC 2011 and if u install iOS 5 on your iPhone 4, iPhone 3GS, iPodTouch 3G, iPosTouch 4G or iPad using Limerian exploit then still you do not need to worry about as there are ways to relegate from iOS 5 to its preceding versions.
Warning : Once you update iPhone 4 or iPhone 3GS to iOS 5 beta there will be no way to downgrade your baseband and you will also lose your unlock. If you want to downgrafe iOS 5 to iOS 4.3.3 or older firmware then you must have saved SHSH blobs (you can find from Cydia for which firmware your SHSH blobs are saved.
Follow below steps to shift from iOS 5 to iOS 4.3.3, iOS 4.3.2, iOS 4.3.1, iOS 4.2.1 or iOS 4.1 on iPhone 4, iPhone 3GS, iPodTouch 4G and iPad.
Step 0:Download iOS 4.3.3, iOS 4.3.2, iOS 4.3.1, iOS 4.2.1 or iOS 4.1 alongwith iTunes and save it on PC, connect your iDevice with your PC / Mac using USB and turn your iDevice off.
Step 1:you need to put your iDevice into DFU mode by following below points.
Press and Hold Home button along with Power button for 10 seconds, release power button only after 10 seconds and release home button after 25 seconds.
Step 2:Launch iTunes once your iDevice is in DFU mode and click OK button in recovery mode. iTunes shall ask your to select the IPSW files to restrore, if you are downgrading from iOS 5 to iOS 4.3.3. the restoration process shall take few minutes and once completed your deivce shall be restarted and your have finally downgraded your iDevice from iOS 5 to iOS 4.3.3.
Step 3:but if you want iOS 4.3.2 or earlier then you have to perform some more steps. Like if you are using a PC with Windows plate form you need to browse to C:\Windows\System32\drivers\etc\ and locate hosts file. For Mac users go to /ect folder to find host file. Once you found the host files open it in Notepad or Wordpad and add “18.104.22.168 gs.apple.com” in host file without quotes.
Step 4: Select your iDeivce from iTunes and press Shift key for Windows and Alt for Mac from keyboard then press restore button. iTunes shall ask you to browse and select the IPSW file. Click Restore button once you select the IPSW file. As restore process complete your device shall be reboots and you have done it.
Note: If you have select IPSW for iOS 4.2.1 then you may encountered some errors while restoring, simply ignore them and you might noticed that your iDevice get stuck in recovery mode with message Connect to iTunes. You just need to download TinyUmbrella and then click on Exit Recovery selection.
This is little tricky but I hope that you shall do it so if you have any issue please do write me using comments options.