To delete your WebSelf account, go to the dashboard, then click on your name at the top right and then on My Profile.
Go to the bottom of your profile page. You will see a rectangle where it says Delete my account.
Note: to be able to delete your account, first of all, you must delete all the sites created with the editor.
You will find the list of sites created, above the Delete your account section. This action is irreversible. You will no longer have access to your invoices or to the editor.