I removed the sleeves, shoulder pads, and collar first. Then, since the armholes were gigantic, I took in a few inches at the shoulders to pull the whole thing up a bit. I also took in the sides. Fabric from the sleeves was used to finish the edges, and the original buttons became an embellishment on my new tank top.
I adore the finished product!
CarissaKnits for more pics and details!