Yep, you can buy that Harbor Freight tool, or "rent" (free if you return it)from Autozone. They are a pretty popular tool item, so check with Autozone before you go there.
Next time I do the brakes, I will disconnect the E-brake cable - makes an easy job even easier,
You need a way to bottom the brake piston - it has little indentations that the tool fits into. Then you screw the piston down. Old school was using a "disk pad spreader" to squeeze the piston back into the bore.
they are right man....i did my rear brakes yesterday...i had to go buy that tool and even then u still need to push hard while turning the piston (CLOCKWISE) to reseat it. Im used to the old school way of using a pry bar and pushing the piston back...not so much the case here. So go buy the tool it will make life much easier for u.