In phrasal verbs the preposition is usually not connected in meaning to the verb. In other words, the meaning of the preposition on its own is irrelevant. I agree, Murphy is good, the Cambridge books on phrasal verbs are also good. Work slowly with phrasals, otherwise you will get them confused. "Change up" can mean change gears in a car to a higher gear (the meaning is not immediately obvious to me). "Finish up" means to finish a meal or an activity to be ready to begin doing something else. "End up" means to be in a final position, as in, "We ended up in Paris after a long journey." I recommend working on no more than five phrasals per session and to learn them by topic rather than by verb or preposition.

Most of the time it means an increase in an action or thought. Example: Hurry up= increase your speed. Wake up= to awaken from sleep, come out of sleep. Sit up= to increase posture. End up, example= you will end up being poor if you spend to much. Shut up, this is a rude way to tell someone to be quiet, but it is a good example that shows you are trying to decrease that persons loud or constant talking. There are many, many more and like the teachers have said you will just have to learn them. Remember increase or decrease , more or less of some action. Look up = you are increasing the level of your head upwards. Hope this will help you understand better and that I didn’t confuse you.

I recommend units 142 and 143 of English Grammar in Use by Murphy. He takes you through common phrasal verbs with up. "Up" usually indicates upwards direction (e.g. change up a gear in a car - go from e.g. 1st to 2nd gear) or it emphasises completion (e.g. end up). You have to learn the usages of phrasal verbs individually and then you can notice patterns, as Elena indicates.

Why do you need a separate meaning of "up"? Those are phrasal verbs - the verb + "up" together convey their own unique meaning which often has nothing to do with the meanings of each of them separately even thought one can see some logics.