How do you change the dipped headlight on a Mercedes a class?

It will vary depending on if you have HID lighting or Halogen Lighting and model year which you did not include in your question. Mercedes-Benz A-Class headlight bulb general replacement procedure: Purchase the correct replacement headlight bulb(s) first, before disassembling the vehicle. See sources and related links below for replacement bulb information. Then consult your owner's manual for the headlight bulb lamp replacement procedure. As simple as it sounds, the owner's manual is the best place to start for bulb replacement instructions and illustrations. You may want to consider replacing both left and right at the same time in order to keep brightness and color equal (optional).