It is not an impossible case where students taking a track change their mind due to various reasons. The most important thing to follow when students considering their study plan, is whether a course is a pre-requisite to another course. 

This pre-requisites can be used to consider which course you can take up or which course you should drop to retake a course.

If you must drop a course, it is recommended to drop a course that is not a pre-requisite in course(s) you will take in the following semester.