John,
Remove the two inset screws and open the sensor where you will see a board with jumpers on it.
Inside, the jumper switches between high, medium and low power. With the jumper in the position closest to the edge of the board is maxiumun, in the other position medium, and removed is low.
Make sure the fine rubber seal stays in place to ensure water resistance of the sensor. It is really easy to do and you can find more information in the forum at
http://www.pursuit-performance.com.au/index1.htm . Send me an email if you need any help.
-Mike