Unfortunately, it’s not possible to delete a free account.
For more info on how to cancel a premium account:
You could try to contact them via http://support.smilebox.com/ics/support/ticketnewwizard.asp?style=classic and ask them to cancel your free account. Please share your experiences.
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.