A LOT OF STAIN ON FRONT GLASS.HOW YOU STOP IT AND CLEAN IT

This suggests you can but shows no screws or fittings
https://www.appliancefactoryparts.com/microwaves/whirlpool/mh6151xht.html

There are videos that may help

https://www.google.com/search?q=whirlpool+microwave+model+MH6151XHT-1+clean+door+glass

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You can use normal glass cleaner or bleach with anything but metal abrasive pads

Smash the inside glass and remove it. Now you can clean the front glass with out a problem.

Harry -
I would first see if your friend has a special ceramic cleaner in his or her cleaning supplies cupboard. If you can't find a ceramic cleaner, the best thing you can do is use hot water to clean the surface. All-purpose cleaners (like Cif) can damage the ceramic glass so it's best to avoid using them.
Also, look in your friend's cleaning supplies cupboard for a metal razor scraper. Use the razor scraper to scrape off any burnt-on food or spills. Do this by holding the scraper at approximately a 30 degrees angle to the cooktop while wearing an oven mitt to protect your hands. If no scraper is available, don't resort to a knife or abrasive sponge as these could damage the ceramic glass.
When the cooking surface is cool, apply a few dabs of the ceramic cleaner (if you found it) in each burner area and work the cleaning cream over the cooktop surface with a damp paper towel. Then wipe down with water and dry with a clean paper towel.
If no ceramic glass cleaner is available, it is sufficient to wipe down with hot water and a soft sponge. Never use abrasive sponges or scouring pads on ceramic glass cooktops. Also watch out for corrosive cleaners such as over sprays, cleaners containing chlorine or ammonia and stain removers - these will just further damage the surface.
For a list of approved CERAN cleaners see here: www.schott-ceran.com

This question was asked almost 2 years ago, but thought I'd respond anyway. On the bottom of your oven door there are slots. Pull out the drawer beneath the oven door so you can work under it. Find something that will fit through the slots, a yard stick worked for me, or maybe a wire coathanger. Attach a paper towel or cloth securely to it and put it though the slots to reach the soiled area. It will take some manuvering. I would not recommend taking the door apart. When I did some research on this some time ago, I read that it can be difficult or impossible to get it back together again.

If you think the window is stained, you ought to see the rest of the inside! Wife is probably right. (wink, wink, nod, nod)
Actually, you can take the cover off, remove the front panel without much effort and clean everything and get a lot more life out of it. Microwaves usually die because of heat related problems caused by buildup of yuck on the guts.
Hope Ya Make your Wife Happy!

Its very hard to take apart the doors They normally have a lot of screws. May have a plastic snap on cover that's covering them up. Some of them are even sealed and can not be taken apart.

Anytime you work on a door you must check it with a microwave leakage meter. The door has metal gaskets and a screen that blocks the microwaves upsetting them will cause it to leak.

This is not a do it yourself repair.

First: do not use this unit with the glass improperly installed. Often, these installations use double sided foam tape, available at any hardware store. Carefully remove the screws in the door being careful to catch the glass. Clean the area where the tape will go with glass cleaner or alcohol. Allow to dry and buff to remove oil and grease. Install the tape and glass. Reassemble.

In most cases you must replace the glass in the door. Sorry i couldnt be of more assistance. Good Luck