Turn off power to the circuit at the breaker
Verify 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 of the existing wire connections
Identify the common wire and the traveler wires
Loosen the terminal screws and remove the wires
Disconnect the ground wire if present
Connect the common wire to the common terminal on the new 3-way switch
Connect the traveler wires to the traveler terminals
Connect the ground wire to the green ground screw
Tighten all terminal screws securely
Carefully fold the wires back into the box
Mount the new switch to the electrical box
Install the switch plate cover
Turn the power back on at the breaker
Test the switch operation from both locations