Darryl is correct about getting to the tweeter at the top of the door panel. You can gain access to the rear of the tweeter by unscrewing the window switch plate under the tweeter. The speaker that's built into the armrest/map pocket can be easily accessed by removing the seven or eight screws that attach the map pocket to the door panel. The speaker at the front of the door panel in that picture looks like it can only be accessed by removing the door panel.
There was an article with step-by-step instructions (and pictures) on removing the door panel in a 968 in the April 2005 Excellence magazine. The article is on replacing the window seals but the door panel had to come off to replace the window seals. Incidentally, if you take the door panels off (which is not hard and it takes just the usual hand tools), you are most of the way to replacing window seals. If your window seals are cracked and ugly, consider replacing them.
--Bob