Turn off the power at the circuit breaker
Verify the switch is off and the power is off with a voltage tester
Remove the switch plate cover
Unscrew and pull the switch out of the electrical box
Take a photo or note the wire connections
Loosen the terminal screws and remove the wires
Connect the wires to the new switch in the same positions
Tighten the terminal screws securely
Attach the switch to the electrical box
Reinstall the switch plate cover
Turn the power back on at the breaker
Test the new switch