From their FAQ (http://www.wuala.com/en/support/faq/c/5):
How do I delete my account?
Please write us an email [[email protected]]. It is important to state your username and send the email from the email address you specified in Wuala.
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.