How to make my monitor vertical instead of horizontal?

Does anyone here know how to make my laptop monitor the primary monitor rather than the secondary?

• I use a monitor plugged into my laptop as dual screen, with different applications on each monitor. Usually my laptop is primary, which is important as when I work from home it will display on my laptop without an external monitor plugged in. However this morning at work it's only allowing my laptop screen as secondary, which means when I get home it won't display properly as a lot of stuff will be on the non-existent external monitor. This includes the display settings, so I'll be unable to change it. Even if I select the laptop as primary display it still displays the external monitor as primary (with all the windows stuff on it) and I have to drag everything over to my laptop screen. Any ideas? I know it's on current events but there appears to be no computer bods on the computer section that can help.

• Answer:

  Would help to know your system. In Windows, I go to display settings, right-click the monitor I want to be primary, and select primary. To change the sides you can drag and drop the monitors too. Make sure to click "apply". You can also click "identify monitor" if you can't figure out which is which. Also it shouldn't be a problem, if there's only one monitor available, your computer should detect this and not try to display to a nonexistent (non-connected) monitor.