The HTC Inspire 4G is the first smartphone available on AT&T Wireless branded as "4G". It's nothing more then an Desire HD locked to AT&T and running AT&T Software.
vincerodrigues91, here is the whole procedure. I'd download the whole page, just to make sure you have it in case it goes offline. Hope this helps, good luck.
Have you tried looking at any of the guides that closely resemble your model? Usually the layout is relatively the same I've noticed. That might point you in the right direction.