Monitors (and projectors) can be managed via the Windows Settings app.
- Click on the Start menu.
- Click the gear icon.
- Click "System."
- Click "Display" in the left sidebar.
- You can change the monitor arrangement by moving the numbered images around so that your mouse properly slides from one screen to the next. (NOTE: Monitor 1 may not be your main monitor. The numbering scheme is for identification only and does not indicate priority.)
- You can change the primary display by clicking on the monitor number you want to be the primary and then scrolling down to click the "Make this my main display" checkbox.
Below is a video that provides a good overview of Windows display management.