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]