Step 1: Open the Menu
Press the Menu button (the up arrow)
Step 2: Menus
Scroll down to Menus then press Enter
Step 3: Tray Configuration
Press Enter to access Tray Configuration
Step 4: MPTray Config
Press Enter to access MPTtray Config
Step 5: Into Paper Size
Press Enter to access Paper Size
Step 6: The Paper Size
Scroll down to your desired size and press Enter.
Your printer is operating in the paper size discerned via an asterisk (*) to the left.