Instructions
Turn on your Wii and select the "Wii Shop Channel" option in the upper right corner of the main menu.
Select the "Settings" option in your Wii Shop Channel menu, then select the "Remove Wii Shop Channel Account" option to erase your shop channel information.
Return to the main menu and select the "Wii" icon in the lower left corner of the menu. This will open the system menu.
Select the "Wii Settings" option in the system menu to open the settings menu.
Select the "Format Wii System Memory" option in the settings menu, then enter your Security PIN (if you have one). Select the "Format" option to erase your Wii's system updates.