these usually need to be cut out with a grinder and replaced with new ones. you might be lucky and be able to drift them out with a punch but could bend
a common fault - seize in to the calipers - its the steel spring collar on the pins that corrodes in the alloy caliper
you can get them out usually - tap round where they fit in the caliper body and then with a quality punch give them a proper whack with a hammer and they should brake free
maybe try a spuirt of plus-gas the night before to help free them up. if your changing the pads anyway it wont matter if they get contaminated with the spray