you will need of course a new radio to install, a wireing harness, and a install kit.
The wireing harness has a plug that mates with the plug your existing radio us plugged into behind the dash and comes with instructions to help you color match the wires to your new radio.
The install kit is a bracket that will mate your new radio to the mounting locations behind the dash trim. They ususally come with the cubby hole pocket that is under the radio since your existing one is actually attached to the original radio.
Both of these are available at best buy or any other automotive audio dealer. For about the same money you could check out
www.crutchfield.com They include these parts as well as excellent vehicle specific directions with the purchase of a radio. Their customer service is top notch IMO.
Disassembly of the dash requires you to remove the ashtray and remove the two phillips screws it hides. There are also 2 or 3 screws above the gauge cluster (spedometer) that have to be removed. From there start at the bottom of the ashtray and carefully pull the trim toward the rear of the car to pop it off. There will be electrical plugs behind there that you will have to disconnect as you go. Keep working towards the door until all the plugs are undone and you can remove the big trim piece.
The radio is held in by a couple of screws that are plainly visible once the trim is off. Remove those and slide the radio out far enough to unplug the wires and remove it. Take care of wireing your new radio to the wireing harness and put everything back together.