If the thread has gone unanswered.. then the "delete" option is viewable. However if someone answers the thread.. the delete option is removed, thats why you don't see the delete button.. You can go back and change the topic or the posts.. or even removed the text from the post all together, Just make sure you indicate why your deleting the topic or post.. and you may need to send a pm to admins asking to have that posted removed.