Turn off the power at the circuit breaker
Verify the power is off with a voltage tester
Remove the existing switch cover plate
Unscrew and pull out the old switch
Take a photo of the existing wire connections
Disconnect the wires from the old switch
Identify the line, load, ground, and neutral wires if required
Connect the dimmer switch wires to the matching house wires
Secure the connections with wire nuts
Attach the ground wire to the ground screw or ground wire
Carefully tuck the wires into the electrical box
Mount the dimmer switch to the box
Install the cover plate
Turn the power back on at the breaker
Test the dimmer switch and light operation