I've searched through the menus but I can't find a way to lower the volume (or completely turn off) the verbal navigation instructions given by the nav system. I know I'm being really stupid here - it must be something obvious that I'm overlooking. Thanks for the help.

 

Set up --> Volume
Alternatively say Volume Up or Volume Down

 

Doh! Thanks! I spent most of my time looking around the navigation menus - where the volume adjust was not an option. I should have spent more time looking at the system wide menus (but I remembered seeing the display brightness setting - I just missed the setting that said VOLUME).