If you have the Premium Gauge Package, and are currently in the "Max Speed" screen, press the "M" button once and then press and hold the "S" button until it resets the Max Speed. This procedure also works on any of the other screens where something can be reset (i.e. Average speed, max rpm, max speed, etc.)
You can also scroll through your other screen options by doing the following: Press the "M" button once (so that the digital numbers are flashing), then press "S" to scroll through the screen options. Once on the one you want, either wait a few seconds until the screen stops flashing or press the "M" button to select it.
Hope this helps!
EDIT: after reading your original posting again, it sounds like you may have already done this... Sorry if I'm telling you something you already know!