The following assumes it's the same as on my two '93 240s....

There are two ways:

first and easiest (although not per the "official" instructions):
apply gentle steady pressure on the whole housing -- it sits in slots that are glued to the window -- and slide it upwards and off the slots. Be careful to hold it straight so it doesn't bind in the slots as it rises. Then when it's off, you can see the tab (that I refer to below) and press on it to take the cover off and access the bulb socket to replace the bulb.

second (this is according to the instructions in the manual):
reach underneath (with preferrably a "double jointed" finger, or a rod or screwdriver best bent at a right angle) and press on a plastic tab that will release the cover and access the bulb socket....

It's not hard once you've seen the process. It's the first time that confounds.

Best regards,