How to debrand Unbrand a Blackberry Bold 9900

Hello all, I’m an enthusiast who wants to get his hands dirty a little. I’ve got a blackberry bold 9900 I got from at&t and I want to remove the Carrier’s restriction. I want it to work as if it was directly purchased from blackberry.
I need links to the tool I need and also some step by step tutorial (as I’m a newbie in this regard:D).