Why do you want to do that? You can study with an H4. In some states, you can even pay the in-state tuition rate with an H4, if you've been living in the state for the required amount of time (typically 1 year). Changing to F1 can complicate things for you if you're planning to pursue a green card, because F1 requires nonimmigrant intent but H1/H4 doesn't.