I am not an expert tech on the matter, so I would not try to direct you on how to take off the door panel. I do know you need an special tool and good knowledge. Just as an example:

The authorized M.B. dealer took off the driver's door panel of a '98 CL500 of a friend of mine to change the light bulb of the seat switch. Upon mounting the door panel back, they broke the double-pane glass of the door. A simple $0.40 light bulb ended up costing them more than $2,000 to replace the door window. Just be carefull...

A. Rosich
S320, 1998
E320T 1995