To delete your account, you need to request a delete from the profile page.

When an account is deleted in Kattis authentication and personal information relating to the account will be removed. Note that before an account can be deleted, all data owners associated with the account will be requested to confirm the delete according to the GDPR. For courses this is typically the teacher or administrator. For recruitment tests it is typically the recruiter. After deletion, submitted code will remain for plagiarism checking purposes, along with minimal information regarding licensing and rights.

Account deletion is permanent and deleted accounts can not be recovered. 

Note that if you have multiple accounts in Kattis and only want to keep one, you should instead request an account merge.