How do I set the window size in Windows 10?

[Windows Central Question]

Since the November update, I find that I cannot reduce any window from full-screen to a smaller size. All I can do is reduce the window to half of the screen (16" display) which is too small to work with or even read or go full-screen. Since I have a weak left eye, my preference is to set my working window to about 2/3 of the display at the left edge, any "waiting" app I leave in another window showing around the edge of the working window. Now I can't! And it is giving me a headache. Help!