Turn off power at the breaker
Verify the power is off with a voltage tester
Remove the switch plate and old switch
Note the wire connections before disconnecting
Disconnect the wires from the old switch
Strip wire ends if needed
Connect the ground wire to the green ground screw
Connect the hot wire to the common or dark-colored terminal
Connect the remaining wire(s) to the other terminal(s)
Tighten all terminal screws securely
Fold wires neatly into the electrical box
Mount the switch into the box
Install the cover plate
Turn power back on at the breaker
Test the switch