Need help changing UCs.

I got into UCSB of the waitlist (hooray!) and I'm currently enrolled at UCSC.

I was wondering if I can submit the SIR for UCSB first and then un-enroll from UCSC (ideal scenario) or if I have to un-enroll from UCSC first then enroll at UCSB.

I think the system doesn't like it if a person is enrolled at two UCs at the same time, but idk.