There’s no account removal option available, and there’s no mention of account removal in their FAQ. However, you can try to contact them via the ticket form: https://support.speedtest.net/requests/new and politely ask for account removal.
URLS:
http://speedtest.net
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.