Instructions
Start the game and in the opening menu you will see either a guest or a Mii line up.
Select the "User settings," which can be seen in the upper right-hand corner of the calendar screen with the "A" Button of the controller.
Choose "Delete User Data" in order to get rid of the old line up. This will allow you to either import or create a new character list resulting in a change of the line up in Wii Fit Plus.