Turn off power at the main breaker
Verify the power is off using a voltage tester
Remove the switch cover plate
Unscrew and pull the existing switch out of the wall box
Disconnect the wires from the old switch (note wire connections or take photos)
Identify the common (COM) terminal and the traveler terminals (for 3-way/4-way switches)
Connect the wires to the new switch terminals:
Hot (line) to COM for 1-way switches
Hot (line) to the common (COM) terminal for 3-way/4-way switches
Travelers to the remaining terminals for 3-way/4-way switches
If the switch has a ground terminal, connect the green or bare copper ground wire to it
If using a neutral in the box (required for some smart switches), connect the neutral wire to the neutral terminal
If using a smart switch, connect required load (switched hot) wire to the load terminal
If the switch requires it, connect the dimmer/sensor wires per the manufacturer’s wiring diagram
Cap any unused wires with wire nuts and tuck them back into the box
Ensure wire connections are tight and no bare copper is exposed
Carefully push the wires and switch back into the wall box
Screw the switch to the box
Install the cover plate
Turn power back on at the main breaker
Test the switch operation
If it doesn’t work, turn power off and re-check wiring against the manufacturer diagram and/or your switch type (1-way vs 3-way vs 4-way)