Instructions
Move your Wii remote cursor over the round "Wii" button in the bottom-left corner of the main menu. Press the "A" button. Then select "Wii Settings."
Press the "A" button with your cursor over the blue arrow twice. Select "Wii System Update."
Choose "Yes" and a message will appear asking you to accept the terms of the Wii system update. Choose "I Accept." Your Wii will now search for the latest system update available.
Read the next message that appears: it will tell you that an update is being downloaded and installed, or that there are no updates available, and thus your console is already up to date.