That clock!! What a pain. To change the trip meter press and hold left button till it changes. Repeat till you have the meter you want. In any mode except odometer, hold both buttons to re-set to zero.
To adjust the clock, you must first be in odometer mode, then when you hold both buttons the clock will flash for adjustment. Neil's instructions after that are correct. When the time is adjusted press both buttons again to exit adjust mode.
Good luck!