Originally Posted by jschmid
Most have a couple grooves in a cross fashion. Some people have used a large flathead to rotate the piston back in, or you can use a specialty tool that has various prongs to fit into your piston grooves:
I did mine last winter, and it was pretty easy. Bought that exact tool from an auto parts store, about $12. One side was really hard to turn, and needed extra leverage, the other side was easier. After you turn the the piston back in, install your new pads, and then once everything is done, and you're back in the car, pull up and down on your ebrake several times, until it feels like normal once again.
BTW, hands down, this is one of the easiest cars to change pads on. Jack car up, take wheel off, remove one bolt, and take out old pads. Press or twist piston back in, and install new pads.
Also, open the brake fluid reservoir, and watch it to make sure it doesn't overflow when you press the pistons back in.