For a detailed guide, see: http://blog.codepen.io/documentation/faq/how-do-i-delete-my-account/
“To delete your account, make sure you are logged in and then choose the Your Settings option from the user dropdown in the upper right. Then click onto the Profile tab. In the lower right of that area there is a red link to Delete Account”.
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.