The phrase "hitch up" usually implies an action to connect or lift something, like hitching up a horse to a carriage or hitching up a backpack. Some antonyms, or words with the opposite meaning, for "hitch up" might include "disconnect," "detach," or "unload." If the context is related to clothing, "loosen" or "unfasten" could be used as antonyms. Alternatively, if "hitch up" is used in a motivational or excited sense, antonyms might include "calm down," "relax," or "settle." It's important to pay attention to the context in which "hitch up" is used to determine the best antonym to use.