When you drag a window to the side of the screen, your mouse must hit the edge before it will happen. You'll get a little indicator and outline when you get that simply release the the window. An Alternative is to use the WINDOWS + one of the four arrow keys.
WIN + UP Arrow, Maximizes
WIN + DOWN Arrow, Minimizes
WIN + LEFT|RIGHT, Cycles the Windows around in 50% splits.
If you do a vertical resize and your mouse hits either the top of bottom of the screen, it will give you the choice to take up the full height of the screen.