I am a 42 year-old, reasonably handy woman with limited strength and a little arthritis in my hands, and I managed this all on my own, just. fine.
Prep: Put an old blanket on a counter, because you will need to put the door OUTSIDE UP, INSIDE down on it with the hinges dangling over the edge of the counter. You will also need degreaser (I used straight white vinegar) if you want to clean things up while you have it taken apart. You will also need glass cleaner (or use vinegar and a microfiber cloth). I didn't want any chemicals on the door, and the vinegar worked great. I kept fingerprints off the glass by holding on to it with a paper towel in order to put it back in place. Also, use several bowls to put the parts (many screws, a few fastener plates) in separate containers. If you have a digital camera, I suggest taking pictures as you take things apart, so you can remember how they went.
TOOLS: Regular Phillips and a screwdriver with a star-shaped head (available in most interchangeable driver sets).
This was for a KitchenAid Superba gas oven.
1. Remove the cover plates over the hinges.
2. Open the door to the 4 inch stop position, and lift slightly, then pull the door straight back. The hinges will come out of the rest of the oven.
3. Put the door on the blanket-covered counter, outside facing up, hinges dangling over the edge.
4. Remove all the screws along the bottom of the door. The little side panels come off once the screws are removed.
5. Lift off the outside plate and set aside.
6. Remove the screws that hold the handle/vent assembly together.
7. Lift off the next of layer (glass held in place by clips, insulation all around). Be careful not to compress or otherwise damage the insulation as much as possible.
8. Remove the next pane of glass that just sits on an aluminum assembly at the bottom of the door.
9. Remove the aluminum assembly at the bottom of the door.
10. You are finally there! Be VERY CAREFUL because now you have sharp, nasty class. The screws (star heads) are insanely tight, but with a little pressure I was able to turn them. Remove all the screws holding the glass in place, and the little fastener plates. Make sure you remember how the little plates go back on.
11. Remove all the glass shards and carefully dispose. If you have tiny pieces of glass (I had some scattered about the inside of the door) you can use a piece of bread to pick them up (press the bread on the tiny bits...make sure to immediately throw away the bread).
12. Put in your awesome new piece of glass that came so quickly and safely.
13. Replace the screws and fastener plates. I did not make it crazy tight like it was before, but I certainly cranked it down tightly.
14. Reverse the process and put it all back together. Be careful with putting the panel with the attached insulation in place. The insulation should not be visible when put together, and it can take a bit of trial and error to get it to stay where it should.
15. Make sure all the screws in the bottom are in tightly. This is how the whole assembly compresses and stays together.
16. While the oven door is off, is a good time to clean it up a bit, replace any lightbulbs that have died, etc. Again, vinegar works really well and won't make for toxic nastiness when you fire the oven up next.
17. Replace the door by sliding the hinges back into the oven.
18. Attach the little plates that keep the hinges where they should be.
19. Do a little celebration dance because you just saved yourself a few hundred dollars in a service call.