I can tell you how I have done it. I do it on a hot day with the car in the sun. This makes the gasket as soft as possible, I then use a plastic knifer to unstick the rubber from the glass. I them start pushing from the inside out. If you have someone to help you by pushing while you work the gasket on the outside. once you get it started at the top and side keep working across the top to the other side. It will lift right out after you till the glass forward. The rear is a lot easier than the front for me.