Don't split the caliper
You didn't mention which GMA Caliper, so lets assume it is a 2 piston caliper (one on each side).
If you split the caliper you will release the fluid and will have to rebleed the brake line.
It's more likely that the pads are held in in by debris and/or some wear into the caliper.
With a flat blade screwdriver gentle get the blade in between the pad friction material and the rotor and pry/wiggle the pads away from the rotor.
You would need the added space anyway because of the greater thickness of the new pads.
The pins are the only thing holding the pads in
Once the pads are away they should loosen, grab the steel backer with needlenose pliers or vise grips and wiggle them out.
Clean the inside of the caliper so the new pads slid in easily and use disk brake lube on the edges that contact the caliper and the piston contact area.