A range hood is mounted above the stove and connected to power and often ductwork, so the safety step is cutting the electricity first. It is greasy and awkward to remove overhead, so a helper and some degreasing make the job much cleaner.
Pro tip: Degrease before you unmount, since a clean hood is far easier and safer to handle.
Watch out: Range hoods are hardwired, so cut the breaker and verify with a tester before touching the wiring.