This depends on the course. Enrollment for many upper level courses is handled entirely through the waitlist, so if there is a waitlist available on Wolverine Access, please add yourself to it.
Enrollment is handled slightly differently for Math 105, 115, and 116. Seats for these courses are opened periodically throughout the registration period (for fall terms this means throughout the summer break). You'll need to check Wolverine Access periodically to see if any seats open up that fit your schedule. If you are still unable to enroll in a section of 105, 115, or 116 once the beginning of the term approaches, please add yourself to the Math 105/115/116 waitlist.