General help

Thanks for your reply. Let me explain: At the beginning of the term, let's say thousands of students enrolled to these six courses but they do not enroll to all of the classes. Then a few weeks later, the advisor approves these courses in our university, some students may add / drop these six courses so the updated list can be quite different from the initial one.

So in the first uploading user list we have no problem. But after second, third or may be fourth updated lists we can't unenroll a student who enrolled a course in the first list with upload user method.

Upload user method just enrolls a student to a course not unenrolls him or her from that course.

How can we solve this problem with an alternative method. And idea?