Can anyone tell me how to adjust or turn off the volume in my COMAND navigation?

while it's speaking use the volume button to adjust. (while in navigation mode press repeat if it's not speaking)

also, with navigation active (put in some dummy route), there is an option for nav volume

iirc (not likely!), it's accessed by pressing one of the buttons lining the screen to bring up the nav options, then poking around the displayed choices until you find it

how's that for precise?

Its easier and way faster the way GAC explained.

Thanks to you both. Works beautifully either way gac advises.
I couldn't find this in the Comand manual - do I need glasses or what?

when did my wife start posting here? I'll have to put you on "ignore" now