To reset you have a button thing sticking out in front of the speedo (on old cars it reset the secondary milometer) press that in while on Mileage setting eg 60k , this resets the computer, re-calculates after 400m (i think) there are a few settings:
distance travelled since reset
average MPG
average speed
distance to refuel
cruise control (optional)
couple more that i cant think of off the top of my head, these are the basics shouldnt be to hard to work them out.
mines a Ph II im presuming they are the same apolgies if they aint.