We are trying to remove Whirlpool microwave model MH7140XFZ/year 1999 from the wall brackets. Is it some trick, because we can not get it from those brackets? Can you please help us?

If this is an above the stove MW, turn off the power to the MW, open the cabinet above the stove and you should see two screws holding the MW to the cabinet. Similar units may also have 2 long screws that are accessed through the front grill and screw to the mounting bracket. Prop or block the MW and remove the wall screws(if equipped) and the cabinet screws. The MW should then tilt down slightly and lift off. You may have to disconnect a vent stack. Be careful, you will still have a power line there and the MW is heavy.