For Mac OS X
1. Open System Preferences, Printers & Scanners.
2. Select the Default Printer in the drop down list.
For Windows 10
To choose a default printer, select the Start button and then Settings . Go to Devices > Printers & scanners > select a printer > Manage. Then select Set as default. If you have Let Windows manage my default printer selected, you'll need to deselect it before you can choose a default printer on your own.
In Windows 10, your default can be the printer you last used. To turn on this mode, open Start and select Settings > Devices > Printers & scanners. Select the checkbox beside Let Windows manage my default printer.
For Windows 7
Open Control Panel, Hardware and Sound, Devices and Printers, right click on the printer and select "Set as default printer"