log into your account, and go to the
my chumby/deactivate a chumby page
then take the chumby that isn't registered to you, and go to it's settings page/chumby info screen.
there you will see it's ID, and it's chumby name that it's registered under. enter those into the page
click 'deactivate'... then reboot your chumby, and you'll get the classic "hey, I'm new, would you register me?" screen then you can go to the normal 'activate a new chumby' page.
edit: I should just go back to sleep, my replies are all too slow today.. must be the wet paint in my eyes *squint*
Cleaning up any loose bits and bytes.