Hi Lila. I moved your post to the help forum.
The simple answer is you can't.
You can edit a post up to 15 mins after you first post but that's it.
Only Mods and Admins can edit or remove posts then - and it's pretty rare of us to do that unless there's good reason.
If you still want to follow this up you can PM me, or another Administrator or Mod
D.