How do I update the title of my thread?

I used to be able to do this and it was easy. But now it looks like I can only edit my individual posts. I’d like to add an “updated see post XX” to the title of this thread: http://www.chronofhorse.com/forum/showthread.php?419215-Small-gift-for-child-leaser-of-my-horse

Thanks!

Edit post -> go advanced

^^You’re brilliant. Thank you!!