It is impossible for a freshman to change his major. Only those experimental classes who don't want to stay there can apply to return to their original majors. Students in the experimental class will be assigned majors in their junior year, so you can choose your favorite major. For students in non-experimental classes, if they want to change majors, they can only minor in their favorite majors, get enough credits and get excellent grades. After taking part in the thesis defense, you can apply for the exchange of major and minor, so that your second major can become your first major.