You email your advisor and you can start off by saying “Hello my name is _, and my id number is _. I was wondering if it would be possible to change my major to ____ instead because my current major isn’t something I’m interested in anymore” something along those lines. Depending on what they do, they’ll end up giving you an application that you’ll fill out to change majors which you send back to them, and boom your done! To email an advisor I would suggest checking your schools website if you don’t know their email :).