From my understanding, it is not too difficult to change your major at UC Davis.
If you want to change your major:
You must use the online Change of Major Petition.
You will need to schedule an appointment with the major adviser of your intended major.
If you are wishing to change your major within the College of Biological Sciences, then you must make an appointment with your new major adviser by clicking the “Schedule an Appointment” link above. You may do so by clicking the “Schedule an Appointment” link above.
Some departments require the completion of prerequisite courses with a minimum GPA before you can change into the major.
You must complete 1 quarter at UC Davis before becoming eligible to change your major.
The approval process will occur online.