right click on the NVIDIA icon in the taskbar on the right, move the cursor up to the monitor you want to change, then a box will appear on the left with a rotation settings option. Easy to figure out from there.
Also, a very basic FYI for anyone running more than one monitor: if you're not sure which monitor is #2 or 3 etc.: right click on the desktop, then click properties/settings/identify. A BIG number will appear on the screen which will correspond to the monitor number in the nVidia menu.
