It's usually Ctrl-Alt and the arrow pointing to where you want the TOP of the desktop to be pointed. So On a normally-arranged monitor, Ctrl-Alt-Down turns it upside-down, ctrl-alt-up turns it rightside up.
It's usually Ctrl-Alt and the arrow pointing to where you want the TOP of the desktop to be pointed. So On a normally-arranged monitor, Ctrl-Alt-Down turns it upside-down, ctrl-alt-up turns it rightside up.