I can't believe I'm unable to figure this out. OK, here's how I understand how this incredibly simple yet mystifying procedure works:
(1) Create a post and submit it.
(2) Notice something with your post you want to change/edit.
(3) Click "Reply" on your own post.
(4) In the URL field, replace "newreply.php" with "editpost.php".
(5) Type newly edited post into post field. Add smilies and graemlins as needed.
(6) Click "continue" at bottom of page.
(7) Enjoy edited post.
What am I missing? I've tried this maybe 10 times and it's never worked for me.