Updating wii firmware
To disable Wii Connect24, access the Wii settings by turning on your Wii.
Move your Wii remote over the "Wii" button in the left corner of the screen, then press the "A" button.
If you'd like to manually update the Wii system software or firmware, access the Wii System Settings and click the "System Update" button.
All native Wii software (including games distributed on Nintendo optical discs, the System Menu itself, Virtual Console games, Wii Ware, and Wii Channels), with the exception of certain homebrew applications, have the IOS version hardcoded into the software.
However, you may realize that, at times, you are better off running an old software version than upgrading to a new version with unseen problems.
In these cases, you may want to stop your Wii from receiving updates.
Nintendo created this system so that new updates would not unintentionally break compatibility with older games, but it does have the side effect that it uses up space on the Wii's internal NAND Flash memory.
IOSes are referred to by their number, which can theoretically be between 0 and 254, although many numbers are skipped, presumably being development versions that were never completed. The only time an IOS is not running is when the Wii enters Game Cube backward compatibility mode, during which the Wii runs a variant of IOS specifically for Game Cube games, MIOS which contains a modified version of the Game Cube's IPL.