It just snaps out. Getting the new one to snap back in was a bigger pain. Get the new one and look at it. From that you will be able to tell how to get the old one out.
When I had to replace mine, I got the replacement from Max (ad to the right). He'll need your interior color code or VIN to get the right one, if they are still available.
The new one will be very hard to fully snap in at the back. That's because the plastic piece that it snaps into will push away from it. With the sun roof, you can get in there and hold it down. I don't know how you can do it without the sun roof.