Instructions
Turn on the Wii.
Open the "Wii System Settings" menu on the home screen.
Locate "Wii System Update" in the "Wii System Settings" menu. This is on the third page of the menu, which you can find by using the "Next" button to flip through the menu pages. Select "Wii System Update" using the controller's "A" button.
Select "Yes" when you are prompted to confirm your choice. Read through the "Terms of Service," and select "I Agree." The newest version of the Wii Menu software downloads, and the Wii reboots. When it starts back up, it will recognize your SD card.