The windows usually stick to the cap after years of being there. Use a stiff plastic "Bondo" applicator to go all of the way around the window to break it loose. A putty knife could work in your case since you are getting new paint. Don't flex the frame too far because the are usually 1/8" safety glass which you can't get without replacing the whole assy.. I don't know if your painter promised to prep it right before so clean all of the glue off with laquer thinner. The windows don't always fall back into the same position and the glue residue shows back in the paint if it is still there. You might also consider un bolting your gas filler door and leaving it with them so there are no excuses on the paint match when it is done. (unless it's 2 tone)