how do you switch your major after being accepted for one already?
You will have resources available at your university that will allow a rather smooth transition. I suggest you make the change by beginning or end of Sophomore year. Junior/Senior years' curriculum is heavily focused on the selected major. Whereas usually, freshman level classes are introductory courses into other fields (often sparking student's interests in other field than originally planned for). You will be supported and guided by the university's personnel if you choice to switch your major during your time at university.