Since you're working with electricity, cut the power at the junction box.
Remove the switch plate.
Remove the wires from the light switch. Insert a flathead screwdriver into the slot and pull out the wires.
Insert the wires into the new switch. It doesn't matter which wires go into which hole.
Push the wires back into the junction box.
Make sure the light switch is properly orientated and tighten down the light switch.
Reattach the switch plate.