EASY EASY EASY!
Open the trunk, and where the plastic lip is (where the trunk lock goes in), remove this strip. There are quite a few little plastic things. Use a flathead and pop these out. Once you have removed this peice, you should have access to all of the screws that hold the bumper in place. I think there are 2 on each side and two in the middle. They're actually something like 13mm nuts or something. Once you have done this, the bumper will be sagging, but will still be held on by the guide rails (one on each side by the wheel well). If you want to get it off, you must pull it/snap it out from these guide rails. These direcftions may not be TOO clear, so refer to this thread, it should have ALL the info you need, including many pictures. GOOD LUCK and let me know how it goes!
This thread has it all:
Loose Bumber W202, MBenz?
You can see 2 screw holes here in this picture, just to give you an idea.