looking at your door, there is a vertical guide mounted w/ 2 bolts at top and one on the bottom, loosen the two top bolts and slide forward.
also make sure the top of the glass is parralel to the roof edge/weatherstrip.
I've been assembling my doors for the last couple weekends (gutted them, got different doors and new GM weatherstrip)
it's a hassle, but well wortht he time to make them right...