Visitor's visa (B-2) & business visitor (B-1)
The B-2 visa is intended for tourists coming to the United States; the B-1 visa is intended for those coming to do business.
Students or exchange visitors who have been admitted to UC are prohibited from enrolling while in B-2 or B-1 visitor status. They must first obtain F-1 or J-1 status.
For all practical purposes, changing from B-1 or B-2 status is no longer possible while in the United States. You will have to leave, apply for a F-1 or J-1 visa and then reenter the United States.
Always discuss your plans with your International Student Advisor before taking any such action.