If you find that the Ctrl+Alt left or right arrow does not work(some versions and systems do not support that)Go to settings and select Landscape in the display menu.
Click on windows icon boyyom left in task bar.
Click Settings, cog wheel in pop up menu.
Click System in the new Menu.
Click Display in the next List.
In that screen there will be a heading saying display orientation.
Scroll the box and select Landscape.