I have owned this microwave for 4 years and it has always been hard to open. Finally, I used some "White Lithium Grease" spray. Sprayed to the inside of the openings of the two interior door latches. Spray to the friction portions of the inside openings. After spraying a little a time, manually move the latches "up and down" to get the grease working. Spray a little more again into the openings (friction portions of the plastic latches). The door now should open a lot easier than before. Have a paper towel available in case of over-spray.
Note: make sure you are not cooking anything or have open food while spraying the White lithium grease. Common sense.