The beta version of the new iOS 4.2 was released yesterday and like everyone, if you were excited about it and went about downloading it, you may have realized that a jailbreak for the new iOS version does not exist as yet and hence you may need to downgrade soon after.
If this situation sounds familiar, folks at RedmondPie have a neat guide to go ahead and perform a downgrade. Do remember that you will need to have a backup of the SHSH blobs for the older iOS firmware that you are downgrading to. If you do not have one, then it may not be possible to downgrade.
So how do you do it? First, download the respective ipsw firmware files from here. Once done, plug your iPhone or iPad to the computer and get it into the DFU mode. Now, navigate to C:\Windows\System32\drivers\etc\ and launch the ‘hosts’ file. Here, add the following line of code
Now, on iTunes, click on the iPhone/iPad icon the left sidebar, and while holding the Shift button down, select “Restore“. You shall be prompted to select the downloaded firmware. Once this is done, iTunes will begin the restoration process. Wait for the process to complete. If you are stuck at the Recovery screen, use the TinyUmbrella application to kick out of the recovery process. The process is done.
Do remember to go back to the hosts file and remove the line of code mentioned earlier.
All credit to RedmondPie for the guide