1. verb To alter or switch something, especially from a usual method or proceedings. In this usage, "change it up" is commonly used. I've had this haircut for awhile now, so I think it's time to change it up. You should change up your material so people don't get bored with it.

2. verb To change to a higher gear while driving. You'll probably need to change up once you get on the highway.

3. noun In baseball, a pitch that has a similar wind-up to a fastball but travels much slower. In this usage, the phrase is usually written as one word. If you throw a changeup now, I think you'll get this guy out.