He should be able to change his major if the major isn’t full he just needs to receive approval from the department that he’s leaving and the department that he’s entering.
From Davis’s website:
“Students planning to declare or change their degree type, declare a major, change their major, or add an additional major are required to complete a Change of Major webform. The Change of Major webform is submitted to the appropriate advisors and dean’s offices involved. If you need to declare a degree type or change of major, submit the major change petition to your dean’s office at least one quarter prior to the quarter in which you filed to graduate.”