It’s amazing how NING makes it very easy to create an account (and point you to prices of their products), but apparently impossible to delete it.
Even on the forum deletion questions are never followed by a simple link or instruction. Perhaps just try to contact them using: http://hc.ning.com/contact/cancel/index.php
URLS:
http://www.ning.com
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.