Turn off the power to the range hood by turning off the circuit breaker in the electrical panel.
Remove the filter, the light cover and the light bulb from the range hood.
To the left or right of the light you should see a metal plate cover. Remove the screws and take away the cover. Underneath should be the wiring assembly.
Test the wires to make sure the correct circuit is off. For this job, a touch-type voltage tester works best. All you have to do is press and hold the button on the tester and hold it up to the black wire inside the junction box.
If the line is dead, disconnect the wiring by removing the wire connectors and pulling the wires apart. If the circuit's ground wire is held under a ground screw, loosen it and remove the wire.
At the back of the range hood wire assembly box you will see where the feed wires enter the body of the unit. Remove the lock nut that is holding the wires in place.
Take the 2-by-4 and span it across the front part of the range hood, using the clamps to secure it to the cabinets on each side of the hood. This brace will act as an extra pair of hands when you are removing the screws that are holding the hood in place.
Before you begin removing screws, check to make sure that the bottom of the range hood was not previously caulked. If it was caulked, take a sharp knife and score it all the way around so it will be easier to remove.
Remove the screws that are securing the range hood to the cabinets. This is when having a cordless drill at the ready could greatly improve your efficiency.
Hold the hood up and have a helper release the clamps and remove the 2-by-4 brace. Then, remove the range hood carefully, making sure that the wires come out of the backside.