Transferring From First Choice Major (Business) to Second Choice Major (PR)

Hello everyone! I was recently admitted to McCombs, which was my first choice when I applied. However, after some interest changes between now and then, I would rather study PR, which was my second-choice major. How would I go about requesting this change? If I have to wait until after the first semester, can I still take PR-related classes in the meantime, or only core-curriculum classes? Is there a way to switch majors before orientation? Thanks in advance!