How do you release the pressure on the brake cylinder on the rear brake pads of a kia spectra 2004?

I did it myself with a large "C" clamp and a block of wood. I used the block of wood behind the caliper to anchor the clamp and used the adjustable side of the clamp to push the cylinder back into its housing. I believe I used a big pair of channel locks or pliers to get enough torque to actually tighten the clamp and force the cylinder back into the caliper.

WARNING: This is a cheap-ass, ghetto way to accomplish this task. You need to be really, really careful to make sure you force the cylinder back straight and not at an angle. If it goes back at an angle it can get stuck and damage the caliper permanently. They also make a specially designed tool to do this repair. This is a more expensive solution, however it minimizes the possibility of doing any damage to your car. Do a google search to find it.