When it asks for how much your clothes way, point to the far right box and use the + or – button to add or subtract pounds. That is the only way I have found. Or weigh yourself neckid! Good luck.
The Wii Fit is a good fun supplement to all of that and a much-needed injection of activity for stay-at-home types, but don’t be fooled into thinking it is the total solution. There’s no replacement for the real thing.