To remove the trim, your best bet would be to push on the white trim clip pins that extend through to the inside of the fender and are attached to the trim. You can get a screwdriver between the trim and fender and pry it off, but depending how good it is stuck on that might damage the trim. The pins snap into thin round plastic cylinders that are pressed into the holes in the fender. Some poeple call them red "berries" because of their color. These red plastic pieces are expendable and can be bought new at any place that sells Mercedes parts. They are cheap and not worth trying to save. You may have to take a utility knife and cut them off of the trim clip pins as they tend to come out of the fender when the trim is removed.

To install, put the new red plastic pieces into the hole in the fender, with the lip toward the outside, and push until it snaps in. Then just snap the trim piece into the holes.