Registration for an exam means that you will have a guaranteed place in the examination room. Once the final registration date for the exam or re-sit period has passed, you can not register or unregister for an exam.
If you have failed to register for an exam, check the schedule for exams to find out where the exam take place or if it is cancelled at the LTU campus where you want to write, you will have an opportunity to write the exam if space is available, however, you will have 45 minutes shorter writing time.
You will need to sign up on the waiting list with the invigilator in the examination room 30 minutes before the exam starts. You must also be able to prove that you are/have been registered for the course and that you don't have an exam resultat (Result certificate). You can do this at My LTU -> Results -> Certificates. There you find both Certificate of registration and Result certificate. You need to show both certificates to the invigilatior.