The diagram can be found at
Open the door all the way and lift it up (press on bottom of door) to lift the hinge pins out, then pull away from the unit (walk backward) to remove it.
Then, the remove the inner plastic shell from the outer plastic shell by prying gently around the outer shell. There are no screws holding it together.
Once apart, you can see the screw (item 8 in the drawing). You can remove the screw and replace the handle. reverse the process to get it together.
Make sure the door is all the way back in tightly and firmly just as it is now or you can have a microwave leak. Work carefull and, if you have a digital camera or a camera phone, take pictures of each step to make sure you know how it goes back together.