If you are a 100 percent sure that you want to delete your account, you can go to the "Delete account" page, which is located under "My Account" - "Account information" page in your account and click the big red "Request Account Deletion" button. But think twice, deleting your account is completely permanent. From the moment you hit the button, you will have only 24 hours to change your mind and cancel the deletion.
Once the account is deleted, you will no longer be able to login, and all of your account information (name, login, password, posts, memberships, participation scores, etc.) will be removed from Packback Questions.