Picked up from http://www.sparkpeople.com/mypage_public_journal_individual.asp?blog_id=2471667
Reset your FitBit:
Dock it, turn the dock over, and hit the button underneath with a pen or paperclip. The FitBit will reboot, displaying the current firmware version and the battery level, then will continue charging. This will not delete any of the tracker data.
Completely erase all information on your FitBit:
1. Put the fitbit on the base station
2. Look under base station and you'll see a tiny hole. That's the reset button that you can push with a small pen or paperclip.
3. Press and hold the button on the Fitbit itself and press the reset button
4. Keep the button on the Fitbit pressed for 6 seconds.
5. Take the Fitbit off the base station
6. Press the button on the Fitbit
7. It should say "Testing" and then "Pass"
8. Press and hold the button until it says "Erase"
Power Off Your FitBit:
Unplug the dock. Dock the FitBit on the unplugged dock, then press the reset button on the bottom.