The accessory lenses fit over the existing lens assembly, they don't replace it. The original lens assembly is not removable.
Basically you have to take the camera completely apart to get at the lens assembly and that's not something most users would be able to do. As far as I know there are no disassembly manuals available, so you'd have to "play it by ear" when taking it apart and that's no easy if you have no experience with camera repair.
Here's a link to a video on how to get the camera apart to replace the LCD, but you'd have to dig a little deeper into the camera to get to the lens.http://www.youtube.com/watch?v=CTBC0bfktw8