How has my clocks in my car changed from miles to killometers?

my car was showing milage now it is showing in killometers why? i have an r reg vectra arctic uk model so how has it changed and can i change it back?How has my clocks in my car changed from miles to killometers?some cars are fitted with a switch to let you decide if you want the readings in miles or km. have a look around the dash and see if there is an obvious answer, failing that have a look in the handbook as it should show you the answer to this problem. The car I had with this was also fitted with a computer which gave me my fuel consumption in mpg or litres/100 km.
How has my clocks in my car changed from miles to killometers?
Read the handbook.
How has my clocks in my car changed from miles to killometers?
What is Milage or Killometer come to it, are they new units of Distance/Weight?