How does this caliper come off?

i have a 1998 chevy lumina that has rear disc brakes,i want to change the calipers on the rear,they are pivot calipers,i know how to change the pads a tilt the cailper up but i dont know how to take off the caliper pivot point to change it.i have went to how to sites on the computer but all they tell me is what i already know (how to change pads) can somebody help me with this problem?