Log in to your account, then use the direct link to delete your account.
URLS:
http://pottermore.com
https://www.pottermore.com/en/profile/delete-account-confirm
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.