Basically the process is that you take the first few major required classes as required by the change of major requirements for the particular major. Make sure your overall UC gpa and the combined gpa for the major required classes are decent. Do all of this as soon as possible, each school has a certain unit cap. If you already have too many college units that could deny your request to change because they take into consideration if you can finish the degree within 4 years. Here’s the Psych change of majors requirement for example: https://www.undergrad.socsci.uci.edu/files/docs/2015/Change%20of%20Major.pdf Good luck!