1) Move seats forward and remove carpet from behind seats.
http://members.optusnet.com.au/kracomputing1/boxster/12.JPG
2) Undo the nuts and bolts that fix the metal cover to the front of the engine to expose the front of the engine.
http://members.optusnet.com.au/kracomputing1/boxster/13.JPG
3) Use a 15/16 wrench and turn clockwise on the adjuster to loosen the belt tension. Simply peel off the belt and be sure to route the new belt the same way.
http://members.optusnet.com.au/kracomputing1/boxster/11.JPG
4) Make sure that the new belt is sitting correctly in the grooves before starting engine to test.
good luck