Its a little tricky you have to roll the window up a little bit, then push the window fowards..um ok fowards would be towards the outer part of the door, furthest away from the cab..then you should be able to feel the rollers and a little spot in the sash/rail that the roller comes out of..i had to wiggle a bit whiole pushing foward and up on the window, and it came right out.. takes a bit of figiting but it will go.
oh yeah...you have to remove the vent window first....