It took me a while to find out how to de-stress myself after exams and it varies from person to person.
Here is a question to ask yourself:
What is it something that I always enjoy doing and that always makes me happy? Is it drawing, hanging out with friends, listening to music, reading books?
For some, it's being quiet like meditation, doing yoga... others, it's hiking, talking a walk in the park, being in touch with nature.
That's something you have to figure out yourself! The earlier you find out what de-stresses you, the easier you will get relaxed once you get to uni and get a job/pursue your career