how do i change the default paper size for everything on my epson wf-2860?

Change the default printer settings on the control panel.

• Press the Home button.
• Go to Settings > General Settings > Printer Settings.
• Change any of the displayed settings, like Paper Size.
• Press the Home button to exit and save.

For Windows computers specifically: You can set defaults for all programs.

1. Right-click the printer icon in the system tray (by the clock).
2. Select Printer Settings.
3. Select the print settings you want as defaults.
4. Click OK.