how do I remove a topic I started?

  Except,  I believe you can only remove your Own posts. 

  If there's any replies, they may remain.  Which can become confusing.  Leading to questions about, "what happened to the original post?" 

  I may be wrong... but I believe only a moderator or administrator could remove an entire post once there's a reply.   So,  contacting one could be required in the advent there was a reply and the Original poster wanted the whole topic to be removed.
    
  A forum member can 'modify'  their own post, including the 'header'  or 'title' at any time.  That option can be used to change it from whatever the original topic was to....   Please Remove This Post   
   
  Without contacting a moderator directly,  it's more likely to be noticed and acted upon.  
    Say... if it were an ad in the buy n sell subforum.    Simply replying to your own post with....    Sold Please Remove    Won't be seen by a moderator Unless they scroll down through the replies.