Not so hard after doing it once...
Just release the air intake cowling after unplugging the sensor by gently pushing it back and down to release the two tabs at the bottom. Then the manual works - remove the housing cover for the main bulb by sliding it up, pull off the electrical connector, twist the retaining ring counter clock wise and remove, pull the bulb out, slide the new one in (flat side up) and reverse the above. Voila - two lights.
1992 Black 500e
1991 Black 300te 4m
1992 Black Renntech 620sl
1979 Porsche 911sc targa