Turn off power at the breaker
Verify power is off with a voltage tester
Remove the switch plate cover
Unscrew and pull out the existing switch
Take a photo of the existing wiring
Identify the common wire, traveler wires, and ground wire
Disconnect the wires from the old switch
Connect the common wire to the common terminal on the new 3-way switch
Connect the two traveler wires to the traveler terminals
Connect the ground wire to the ground terminal
Secure the switch into the electrical box
Install the switch plate cover
Restore power at the breaker
Test both switches to confirm proper operation