Yes the headlight needs to be removed.
Before I go into that process, can you handle the removal.
If not I attached a web page.
The corners are really only held in by a little pressure. Once you look at your's you will see a little lip on the bottom.
Ignore that, you will need to apply a little pressure to the top part of the corner.
Push from the back out and the little plastic pins will pop free, a little oil wont hurt on the pin.
Careful when pushing the top pins, because if you go to fast you will crack the little shelf off which holds the bottom of the corner.
If you do, don't worry, it will work with the little shelf broken.
Here is a website to help you remove your headlights:
http://www.bombaydigital.com/boxster/projects/headlamp/
Scott