You can shorten it from the cuff end relatively easily, it is a simply alteration if you don't move the placket. Shortening by a large amount may shorten the sleeve placket too much so you might then want to move the whole placket up. This is a bit more complicated than just moving the cuff up, but isn't too hard. It does require reconstructing the placket. Shortening from the shoulder is not really recommended for shirts; for a start the taper of the sleeve means that, after shortening, the sleeve head will likely end up smaller than the arm-scye you're trying to attach if to. You would then need to also bring in the chest of the shirt in an attempt to make the scye smaller. Adjusting from the shoulders also means flat-felling the arm/body seam, as well as opening and reflat-felling at least part of the side/under-arm seam, which can be quite tricky work.