Hi,
Leave all the calipers sitting on the rotors.
Pull one caliper remove pads, use a Large C-Clamp, cover caliper piston with old pad install C-Clamp over old pad and caliper and Slowly tighten clamp, that will push the piston in.

AR is correct , however if the caliper , (rear only) includes the parking brake , you need
to turn the piston as well as compress .
In front , if its very difficult using a c clamp , its time for new calipers.
Normally you can push the caliper back with a large flat blade screwdriver prying
the old outer pad against the caliper thru the "peep" hole at the middle of the caliper assembly.
This is done with the caliper in place , just as you found it when you pulled the wheel off.