You must change advisors. During the academic year 2001-2002, I will be on sabbatic leave. Because I will be away from campus, you must have a different advisor next year. In your registration meeting, we can discuss various advising possibilities for you. However, the farther along you are in your studies, the less opportunity you have to complete all of your requirements in eight semesters.
Students DO change their minds, however.
Because you have been taking courses in both areas, you have probably already taken the lower-level requirements and may be able to switch easily. Turn your minor into a major. If you find yourself with two majors, consider writing a single senior comprehensive project that combines both areas. Joint comps are very common, and can be very desirable because they take advantage two areas of expertise. Make sure that both departments agree with your plans and that you have enough separate credits in each department to qualify for a major.