You have to send an email to email@example.com and provide them with your username, date of birth and postal code and they'll apparently delete the account for you. That's not very user-friendly.
However, as one of our visitors pointed out, they're not too keen on responding. You might have to send them a few requests.
If you can't find any contact info and still wish to ask something, for example a question about what exactly is deleted, about data retention, etc., you may contact the domain owners using this info.
If you signed up for Spotify using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Spotify. Click the icon below to find out how.