Windows 7 & 8:  

Click on your [Start] menu button 
Select Control Panel
Select and open the Devices and Drives option 
Right click on the Default Printer, and select Printing Preferences
Look for the Paper Size option 
Change the Paper Size to A4 (will not work on Letter) 
Click [OK]  

  

Windows 10:  

Click on your [Start] menu button 
Select Settings
In the Search field, type Control Panel
Click on Control Panel
Select and open the Devices and Printers option 
Right click on the Default Printer, and select Printing Preferences
Look for the Paper Size option 
Change the Paper Size to A4 (will not work on Letter) 
Click [Ok] 

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