You can't really declare a major online. To declare a new major, go to the advising website https://asitauth.colorado.edu/?pg=aHR0cHM6Ly9hYWNwb3J0YWwuY29sb3JhZG8uZW... and make an appointment to add/change major. You can scroll through a list of majors and choose the one you want. Then, it should give you a schedule of times of the major meetings for that major. You have to go to a major meeting to declare the major.