Not having these nice toys on mine I can't fully say what is involved but
Units of measure
To toggle between metric and imperial units, scroll to this display and press the SET/RESET button.
Toggling the units of measure using this display will affect the following displays:
• Distance to empty
• Average fuel consumption
• Instantaneous fuel consumption
• Average speed
• Outside air temperature
• The temperature display in the automatic climate control.
The units of measure for outside air temperature and the automatic climate control can be toggled
independent of the other displays.
to the left of the steering wheel you should have the multi function lever. you should have 2 controls on it: the rotary control and the SET/RESET button.
scroll the menu, using the rotary control, until the board display shows "YOUR SETTINGS >> SET/RESET". then press the SET/RESET button once. the car has to be stoped (motionless) when you do this, otherwise this menu will not be available (it is a safety feature).
after pressing the SET/RESET button, the menu will change and you will have to scroll (using the rotary control) to the option named "MEASURE UNITS METRIC". press the SET/RESET buton again, set the desired option, and then scroll to "YOUR SETTINGS >> EXIT".
as Richard told you, this will change many things, not only the temperature.
I get the impression you're happy with the metric setup (MPG etc) but want Celsius displayed rather than Fahrenheit.
To change to Celsius toggle through the menu until only the temperature is displayed. Press and hold the set/reset button until the display changes to celcius.