C250 - Changing Audio Volume
You will need the ADMIN Card to log into the menus

Press the M/ button (a padlock will display) swipe the Admin card
Select the SYSTEM icon and press the OK button

Select the SYSTEM icon and press the OK button

Use the arrow keys and navigate to the VOL option. In here you can set the volume to LOW, MID or HIGH

When you have set the volume you need press the ESC key and save the changes

Finally press the ESC key a few times to exit the menus.