If you regret having registered for an exam, you can cancel it until a week before you are to take it.
If you are a guest or an exchange student, you must contact the Examinations Office (Odense) or Student Services (other campuses) to do this. The exemption to this rule is students at the Faculty of Engineering. You must cancel the exam within the first few weeks of the semester.
If you are a full degree students, you must cancel exams through student-self service.
If there is less than a week to the exam, it is not possible to cancel it. An option is not to show up for the exam. Note then, that it counts as an exam attempt. You have 3 attempts for each exam.
Out of consideration to your fellow students and the general planning of exams, you should make sure to notify your study secretary if you are not able to make an exam, even if it is too late to cancel the exam.