There are a couple speedo recalibrators available. The yellow box and another. Do a quick search and you'll find the info.
On my 2000, the stock gearing was already off by 10% on the speedo, the revised gearing took it to 14%. So you really need to recalibrate anyway (I haven't yet).
The speedo recalibrators can do the conversion for you (just set it up that way and remember that it is different), but I also think there is a way to hold down buttons when you key on/off or something to get it to switch. A search of the archives here, or over at
ROGUE RC51 Owners Group of United Enthusiasts should net you an answer.
Enjoy the bikes.