Turn off the circuit that runs the garbage disposal at the breaker box. Attempt to start the disposal to ensure the electricity is off.
Remove the screws that secure the cover plate on the bottom of the unit and place the cover plate off to the side.
Disconnect the ground screw and separate the green wire connected to the ground screw. Remove the wire nuts from the two wire leads and separate all of the wires.
Loosen the clamp that secures the dishwasher discharge hose to the side of the disposal with a screwdriver and then pull the hose off the disposal. If you do not have a dishwasher installed, you can forgo this step.
Support the bottom of the disposal with one hand and rotate the three-tab mounting ring counter-clockwise until the disposal disconnects from the mounting bracket.
Remove the three retaining bolts on the three-tab mounting ring and pry the ring off the sink with your hands.