You can only deactivate your account (although it’s named ‘deletion’ unfortunately). See the link below.
If you think this is not enough (and at AK the site is blacklisted because no genuine deletion is possible), then our advice is to request true deletion using: http://www.readability.com/contact
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.