There are 4 small holes in the corners of the HU. You need 2 small U-shaped tools to release the locking mechanism, and the HU will slide out. You can pick up the tools from Wal-Mart for $4, or you can make some yourself using a coat hanger.
For a newbie, I'd highly suggest a car stereo installation kit from
www.crutchfield.com. They're vehicle specific and come with the removal tools, extremely detailed instructions, and all wiring harnasses you'll need (including the factory amp bypass that you'll want to use in your car). It'll cost $20 or so and be money well spent.
