You posted in the Garmin Connect sub-forum which concerns the Garmin Connect web-site, but it sounds like you are asking about the units displayed on your device.
If it is the units displayed on your device, then <settings> <system> <system setup> then press enter till you get to the setting for "units format".
If you want everything in metric, then select "metric" if you select statue UK, then I think.... elevation is metres, distance is miles, and temp is Celsius.
