Remove the screws from the existing switch and pull it out from the wall. Straighten the wires coming from the wall. Twist a wire from the switch onto a wire from the wall and snug the connection with the needle-nose pliers. Use a barrel crimp to connect the green wire onto the bare copper ground wire. For this installation, it doesn't matter which color wires you use to make your connections.
Some building codes require that ground wires be connected with barrel crimps.
Cap the connection tightly with a wire nut. Repeat the process for the other two wires. Push the wires back into the box, screw the switch into place, and replace the cover. Turn the power back on at the circuit breaker.