stefan, buy a new one, you'll destroy it taking it off, we always do(as did the body shop that did my car and they put it back on all deformed and BENT!!). if you get it off without deforming it you are a better man then i sir
and usually we just roll down the window, unscrew it(usually attached at one end) and yank. set the new one into place and screw it down.
jeremy