Have you read your owners manual?
There are two settings, 1 and 2. On setting 1, it resets everything every hour or so, whereas on option 2 it keeps all the info there until you reset it.
Under the Trip computer stalk is a little button, press that to change between 1 & 2, you will see the number 1 or 2 on the screen. You can only change this when the screen is on average fuel consumption or speed iirc.