This is done from underneath the car and can be accomplished in only a few minutes.
You will need a small ratchet, extension (about 10" will do) with a u-joint and a 7 mm socket (I think it is 7 mm). There are two screws holding the assembly in place.
The entire essembly needs to be removed and there are 3 metal clips holding the lens in place. They slide off. Simply remove what is left of the old lens and pop in the new one.
This is for the clk 320.