This instruction goes for all Datanta and Amistarium variants (com, co.uk etc.). The only difference may be that you need to have the wordings in your own language (such as Spanish).
Be logged in on the site. Click Edit profile on the main page. On your left, click Account Settings. Scroll and click the deletion link.
If you signed up for Amistarium using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Amistarium. Click the icon below to find out how.