If your monitors have switched for some reason here is how to switch them back!
Looking at the pictures on the right.... Right click on the desktop and chose Display Settings. Click on "Identify" to see which screen is which. (These numbers do not really matter - they are just identifiers.)
Click AND drag the numbers to rearrange your monitors. YES you can put them on TOP of each other but you probably do NOT want to.
You probably just need them next to each other.
Don't forget to click on "Apply"
To change which one is your main screen with all the icons on it...
Select the screen you WANT as your main screen the SCROLL DOWN to where it says "Multiple Displays" Check the box that says "Make this my main display"
Click the dropdown menu also to either extend or mirror your displays.