Please see the manual section of the support website for details on your specific LCD screen.
This is the process for the C965 display:
1) You turn on the display and press the up/down buttons at the same time
> this will get you to the basic parameter settings
2) The first screen you see is the data cleanup (this erases the trip meter), shortly press the middle button to go to the next setting
3) The second screen you see is the display brightness, shortly press the middle button to go to the next setting
4) The third screen shows the unit of measurement, please use the + and - buttons to change between imperial and metric.
5) Once you selected the metric unit of measurement shortly press the middle button a few times until you're back on the main screen.