Because of this you will have to see if there is an open registration for examination on the selected course.
Go to https://www.student.ladok.se, select a course and then click on "Result". On this page you can see if there is an open registration for examination on the selected course.
If you don't have the option to do it yourself you must contact the course administrator so they can do it for you.
Don't forget to look at the quick reference guide which includes registration for examination.