Well, I finally got around to updating it. I was very lazy and neglected to document the process of transforming it. Sorry.
But I can tell you what I did before I reveal the finished product. :)
I removed the collar, the sleeves and the buttons. I took in the sides about 1 inch, took up the bottom hem about 6 inches, sewed closed the part that had been buttoned, and put darts in the front. I also turned the former bottom hem of the dress into a sash.
I like to think that the finished product is an improvement!