Open the oven door halfway.
Lodge a screwdriver into one side of the spring-loaded hinge. This will keep the hinges extended out and prevent them from snapping back into their slots in the oven frame while you're working.
Place one hand on either side of the oven door and pull it off the hinges. You may have to wiggle it back and forth slightly to free it from the hinges. Place the door on a flat surface with the door interior face-up.
Remove the screws on the interior door that secure the inner door shell to the main door body. Also remove the screws that secure the handle to the door. Remove the inner door shell.
Lift out the old window pack from the door. Use a putty knife to scrape off any large chunks of debris and scrub the interior of the door with a scouring pad and a bucket of soapy water. Rinse the door well with clean water and let it dry thoroughly.
Fit a new window pack into the door where you removed the old one. The window has a pre-installed gasket so all you have to do is set it in place. Replace the inner door shell and fasten the screws. Reinstall the handle and insert the door back onto its hinges. Remove the screwdriver and close the oven door.