If a class or section you would like to take in the fall or summer semester is full, you can contact the instructor of the class to see if they are willing to overload the section you would like to take. There are many reasons why this might not be possible (not enough room in the lecture hall, not enough lab benches in a lab section, not enough resources for all students etc.), but if you do not ask, you do not give the instructor an opportunity to say yes.
If the answer is yes, you and the instructor need to sign a Course Wavier Request form (available in our office and at the Registrar’s Office). Once signed, you need to submit the form to the Registrar’s Office (third floor of the UC) and they will put it on WebAdvisor for you.