From ModMyi - Wiki

This is the continuation of our Pwning 2.0 beta guide. If you have not followed the steps on page 1 please go back and follow them before continuing.

We are now going to load the custom 2.0 Beta .ipsw that you created on page 1 of our guide on to your iPhone / iPod Touch. Start iTunes. If you remember your iPhone is plugged in and in restore mode. If it isn't you'll want to plug it in and put it in restore mode before continuing. You can do this by holding down the Home button and the Sleep button until it has the "Connect to iTunes icon", Do not release when iPhone Shuts down, keep holding it

iTunes will prompt you to warn you that your iPhone / iPod Touchis in restore mode. Select OK

Your iTunes will show the following screen. Hold the option key and select Restore.

Browse to the custom 2.0 beta .ipsw you created on page 1 of this guide. Select it and click Open.

iTunes will go through its normal restore process.

iTunes will give you the old your iPhone / iPod Touch has been restored blah blah blah screen select OK.

Once your iPhone / iPod Touch has rebooted you will be on version 2.0 Beta.