What course is it? You should be able to drop or add courses as long as it doesn't bring your ECTS below the minimum required. If you're a freshman, dropping a course likely won’t be an issue, since most of them carry 5 ECTS, except for Physical Fitness. However, you’ll need to visit the registrar before the deadline. If the deadline has already passed, you can explain that you weren’t aware of the process—they might be understanding.