If it's liphooked, you just remove the hook like with a fish, turning the hook somewhat to get the barb out. Just make sure to approach it from behind, step on its shell, and use gloves + needle nose pliers.
If it swallows the hook, you're better off cutting the line. If it's a treble hook on a lure, you're better off just using needlenose pliers to remove the hook from the lure.