2 switches in one box in bathroom
use a non contact voltage detector (its a small "pen" like instrument that when put near power will beep) to confirm which switch the power comes from. black will be your power wire, white is neutral and red is for the switch. (any one will zap you if not careful)

switch the breaker to the OFF position (Make sure you've got the right one!!) and replacing the switch is as easy as unscrewing the screws and reattaching the wires in their corresponding positions.