Well, first things first. In order to get the trim off, it's just a matter of prying it off. Be gentle, of course, and make sure you get it all around. It's one piece, around the ignition, air vents, stereo, and HVAC controls. The stereo is mounted with brackets and the the brackets are put into the dash with four hex/philips screws. I recommend getting a hex socket for them because mine were on pretty tight and couldn't get them out with a philips screwdriver.
If you have the 7 speaker premium audio system, then you have a factory amplifier and will need a different harness with preamp outputs and also make sure that your stereo has pre-amp outputs, or you will blow your speakers like I did. Here is a link for the Metra harness with pre-amps:
http://www.crutchfield.com/p_1207081...0-8112&tp=2977
If you're looking to put in aftermarket speakers and amp, then you will have to basically rewire the whole car or replace the factory amp.