That screw that covers the pad pin is always a tight booger, use the biggest screwdriver you have in that slot, else it tears. Pouring a few cups of hot water carefuly over the local area will help to loosen it. If all else & I mean all else, fails, use a centrepunch to
carefuly drive it round to start. Don't be tempted to over tighten it when you put it back in.
Once you have this out, there's about ten minutes work to remove the old pads, copper slip & replace the new pads.
If your pistons don't slide back in by finger pressure, there is a case to look at the caliper as well, cleaning & possibly seal replacement. At this point you need friends of substance.
Once done, after the first time, this is a pleasant little way to spend a half hour out on the garage doing men things & saving your self money.