Summer Add-Drop Procedure
All registration adds require the instructor's signature of permission, so it normally makes sense to wait until you and your professors return to campus to do the paperwork.
However, you can start the process by emailing your advisor and the professors of the courses you want to add.
Tell your advisor your plan and ask for any advice about it.
Email the profs of the courses you want to add, and ask if the prof could please save you a seat in the class.
Then, depending on what your advisor and profs say, as soon as possible after you and profs get back to campus, use the add form [pdf] to collect the instructor signature(s) to add approved classes, and drop (online) the classes to be dropped.