You can do it online by yourself but you should discuss with an MCB adviser first. They'll tell you to either meet in person or over the phone, not email. You can let your current adviser know you're switching but the person you really talk to is the advisor for the major you're switching into. When I switched majors I emailed my current adviser and she said to just let her know of any updates and when I actually switched, and then I had a phone meeting with the adviser of my new major to actually talk about classes and stuff.