It was easy ... as the creator, up near the top before the first post but below the thread title, here are white boxes with blue letters on the right ; one says "Unwatch" and the other says "... (down-pointing triangle)". The right-most one is a pull down menu, which let me edit the title
(Which was originally "Possible to edit a Thrd Title?". Can't delete the first post though, nor the thread by myself, although I can edit the first post.