While looking at your home screen, pinch in with two fingers. This will open the editing function for your home screens. At the top you will see the screens you currently have. Swipe them over and the last panel will be blank with a plus (+) sign in it, tap that to add a panel.
You can also press and hold on a blank spot on your homescreen and it will show you your homescreens. If you can add another homescreen there will be a + sign. On my M7 the max number of homescreens is 5.