First, just an FYI, those are your the fog lamps. If you have never changed the bulb before I suggest you remove the anti-noise panel rather than work thru the trap door.

The panel is held on by a total of 10 fasteners. Three around each wheel and 4 in the middle on each side of the center line. The rear two center line fasteners are shared by the rear (smaller) anti-noise panel.

Be sure to examine the bulb, housing and wiring for any evidence of over-heating which is a common problem. Removing the panel aids in the inspection. Also, MB makes a wiring harness repair kit for this problem.

Removing the panel also provides you with the opportunity to inspect that area of the car.

Good luck.