Download the required IPSW file to which you want to downgrade to

Step 2: Once youve downloaded the required IPSW file, its time you put your iPhone, iPad or iPod touch into DFU mode.

Turn your device off.
Hold down the Power button and the Home button at the same time for 10 seconds.
After 10 seconds, release the Power button but dont let go of the Home button, your computer should detect a new USB device.

(At this point, your devices screen should be off, if thats so, then youve successfully put your device in DFU mode. If iTunes logo shows up, youre in Recovery Mode, NOT DFU mode.)

Step 3: Here comes the tricky and the most important part, youre going to fool iTunes into thinking that its in contact with Apples servers, whereas were going to change that to Sauriks server. In order to do this, follow the steps given below:

Windows users:

Navigate to C:\Windows\System32\drivers\etc\ and locate the file named as hosts.

Mac users:

Mac users can access the hosts file by navigating to /etc/ folder, which can be found through Go > Go to Folder from within Finder.

If youre on Windows, then open the hosts file in Notepad. If on a Mac, then open the hosts file in TextEdit, and add the following line at the very bottom.

74.208.105.171 gs.apple.com


Just save the file and close Notepad or TextEdit, and youre all set for the downgrade.

Step 4: Launch iTunes, choose your device from the left sidebar. Hold down the left Shift key if youre on Windows or hold down the left alt key if youre on a Mac and click on Restore, do not click anything else! A new window will pop up asking you for the location of the IPSW file.

Navigate to the desired firmware to which you want to downgrade to, in this case it can be either iOS 4.3.3, 4.3.2, 4.3.1, 4.3 or 4.2.1. Once you find the required IPSW file, click Open and let iTunes do its thing.

If you see an error screen pop up just ignore it.

Hope this helps!

4.2.1 firmware: [ Register or Signin to view external links. ] (top right hand corner and pick if you're on windows or Mac.)
4.3.3 firmware: [ Register or Signin to view external links. ]