Brake pads jammed on rear cycle wheel

APOLOGIES!! I COULD NOT FIND A CORRECT CATEGORY OR SUBCATEGORY SO I AM AFRAID I HAVE JUST GRABBED AT THE FIRST THING THAT CAME TO HAND AND HOPE THAT I MIGHT FIND SOMEONE WHO KNOWS ABOUT CYCLES!! Something must have happened while my husband's bike was being carried on the bike carrier on our car, because when we took it off last night we found that the brake pads on the rear wheel have jammed tight onto the rim of the wheel and we don't know how to release them. There was no problem with the brakes before and there is no sign of the wheel having been buckled in any way. Alas, we do not have a manual for the bike. I am hoping that there is something very simple that we can do to remedy the situation, and I would be extremely grateful if someone could explain what we need to do!!