(no need to submit the form to this office)
Log in ->student service(학생서비스) ->class/grade(수업/성적) ->class(수업)->정규학기 수강취소->choose the course you want to drop -> fill out the reason -> click save -> click ’취소’
Course withdrawal will be complete after the prof. approves

Keep note that course cancellation can not be changed once the prof. approves