You can delete your account inside the application: In Profile - Settings - Account - Delete account

Unsupported phones and versions: In order to delete your account contact support from top right and make a request to delete your account.

The support will require your username and email address in order to verify the requests authenticity. They might ask also for additional information.

Please note! When account is deleted with all its content, it can't be undone.
Note also! If you have Suunto app in use with the same credentials, all that information will also be lost and it can't be recovered.