In the Q&A section, you will find that you need to use the contact form (see link) and request account deletion. Not 100% neat, but good enough.
URLS:
http://www.ted.com/
http://support.ted.com/customer/portal/emails/new
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.