Kevins right, and you will need to get some butyl tape to seal the new one back in. Take all the nuts off, start pushing on the window flathanded, spreading the preasure over as much windo area as possible, and the old butyl will start to let go. just clean up all the old butyl, apply your new butyl to the new window, press into place, and start all the nuts back on. Work your way around the window, slowly tightening all the nuts a little at a time.