First make sure you know who your current advisor is. You can find this out by logging into ISIS. Then ask your prospective advisor if they are available.
If you are a junior or senior, you must have faculty advisor from your major program. Ask the receptionist in the Student Development Center (3124 SC) if you need an appointment to make the change. If you are a first or second year student (E1 or E2) you may have an academic advisor from the Student Development Center or you may have a faculty advisor. You do not have to have a formal advisor to get good advice. While only the advisor listed on ISIS can authorize your registration, faculty and SDC advisors are all willing to give you advice. Just ask!