In order to close your account you'll first need to login. After login locate the "My Account" menu item in the top right of the page and click the "Update Login Information" in the dropdown. At the bottom of this page you will see a button to delete your account.
We're sorry to see you go. We'd love to hear why. Send an email to firstname.lastname@example.org and let us know. We won't try and change your mind we're only looking at how we can improve. Thank you!