Even if your account is deleted and you begin a new one, your posts will remain under the alias "Guest". It is not possible to go through and delete all of your posts unless you do it manually, deleting topics and threads and each and every post.
If you would like to start a new account and wish for me to delete this one, shoot me a PM with an okay to delete this (it will make the posts you wrote just like every other guest, it'll be anonymous and no one will know it's you) and let me know what your username will be so I can approve you.