its super easy, i'll try to describe it the best i can with the pics i have, so here it goes...
1. With both hands grab firmly the black trim around the radio...
2. PULL BACK towards you, on the trim. you should feel it pop out
3. There is another small trim piece that needs to be pulled out, it is located at the bottom of the the radio.
4. There are four 10mm bolts that hold the radio in that need to be removed.
5. Once bolts ar removed the radio should pull right out!!!
This is the way i did it to install my SIRIUS reciever, it may not be the best way, but it worked... I hope this helps you, sorry for the bad illustrations...