Instructions
Use the Wiimote to navigate through the game's main menu. You will see a list of all the Miis (user avatars) saved to the Wii. Each Mii has its own separate license. Select the Mii you wish to use and begin the game. Keep playing until you wish to switch licenses and are not currently racing.
Return to the main menu by selecting the menu button on your screen. Select the "License Setting" option. Select "Change Mii."
Click on the Mii you wish to switch to and press "A." You will now be playing with a different license.