Kirsty is correct that http://www.wikitree.com/wiki/Closing_an_Account is where to go for instructions if you're a member.
If you're not a member -- if someone else has put your name on WikiTree, perhaps a distant cousin of yours -- see http://www.wikitree.com/wiki/Privacy_conflicts_between_users and follow the link from the bottom of the profile that has your name on it if the Profile Manager won't remove it.
