If your rotors are worn, the outer edge will have a "lip" where the pad doesn't wear the surface of the rotor. It is recommended that you have your rotors turned or surfaced by a machine shop or auto parts store when your pads are replaced, generally a $10-$20 job (each). However if the rotor surface is smooth, I usually just replace the pads. Do this at your own risk! If the rotors are grooved, you must turn the rotors for proper braking.
Good luck, I have not replaced the fronts yet, but the rears can be difficult. Do a search & read the instructions here, they are very good.
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