Donwload the firmware from here: http://www.felixbruns.de/iPod/firmware/ - Make sure you download the iPad 2 one
Then with the .ipsw file, open iTunes with the iPad plugged in. Hold shift and click the Update/Restore button. It will then let you choose the firmware.
A couple of things 'tho... Remember to sync your iPad first, to create a backup file, and then, when you've downloaded the IPSW file, you'll need to remember to Shift/Restore on a PC or Alt/Restore on a Mac to point iTunes to the file you've just downloaded for the restore/update. Here's a link covering that as well: