like SumAccordGuy said...if it is a slotted piston (rear only if memory suits me) find something (big $@#%^ screwdriver) to turn it CLOCKWISE back into the caliper. The fronts you can usually use the old brake pad, put it on the piston and then use a clamp on the back of the caliper and the old pad, slowly tighten and it will compress, watch you dont pinch the piston boot or your screwed, and watch your resivor as well, you dont want to start leaking DOT4 everywhere...if you take your time, and pay attention to details, its a really easy job.