Pull the pin out, slide the rail outwards (may need persuading with heavy tool) and lever the pads out. Remeber to release the handbrake first
When the pads are out, DON'T push the brake pedal. Try pushing and pulling the caliper....it should slide freely and easily with little effort on its sliders. If it doesn't, you'll need to remove the bolts which act as the pins and clean them up with wet & dry and some WD40. Then apply copper grease and refit.
Ensure you've got the locking rail in the right way up...did mine half asleep once and put it in upside down. Pads fell out when I got to work next day...not good.
Remember the pistons don't just push back in, they wind aswell. There are tools to make this easier, or just use a big screwdriver on its side and lever it while swearing a bit.
MAy also be worth cleaning up the area the pads sit and making sure it's all smooth and grit-free to allow them to move.
Only thing I struggle with is anti-rattle clips, which I can never get back in. I've left them out for 5 years now....all that happens is that it clunks when I hit the brakes while reversing


