Great title to your post
You place the palm of your hand on the window on the inside, and gently but forcefully push outwards until the window pops out.
Replace the seal/whatever you want, and then get a length of that flat type nylon rope, wrap it around the seal. Get some liquid soap to help, and apply pressure on the glass on the outside pushing in while you use the rope to pull the rubber seal into position.
It may take a couple of tries, but it is not that terribly hard to do.
Good luck,
Keith