I've UN seized calipers before. They can be a pain to do, but makes a difference when they are done. You will need a seal kit. These are availiable from toyota, or one of the traders on here. Chances are that the auto adjuster inside the caliper may have failed. These can be tricky to put back together but not impossible. If your not confident or do not have a wide selection of tools I would not advise you to take on the task. Also check that your handbrake cables are free. They do seize up very easily.