First click post replay
Then click Attachments (The Black Paper Clip)
A new window should come up
Then pick one of the rectangles that say "Choose File".
Then find your Toribash directory.
Go to the folder called replay.
Find the one you want.
Click Open. OBVIOUSLY.
Hit Upload.
At the bottom of the new window, there should be a button that says "Close This Window". There is one on the top right corner too.
Write something and submit Reply. (Wow, it caught up in time)
P.S. Curse you, this took about a half hour of my time.