You need a special tool, but you can get away with a small allen key. There are two little small rectangles on the left / right sides of the radio face. These flips open sideways. Use a flashlight to see in them; you'll see little 5 sided holes. Stick an allen key in there and get one that 'jams' in place. Turn counter clockwise making sure the screw in the radio is actually turning out. When you loosen them both off, the radio will easily slide out.
However, the serial needs to go to the dealer, and the dealer will charge you more for a radio code than a cheap CD is worth usually. Instead, try looking through everything in the glovebox, manual, etc and look for the radio code. Its on a credit card sized slip, but might be written down somewhere.
There is a slim hope its written on the radio itself, but unlikely.