The Nintendo Wii is a highly modifiable console. It can be "hard modded," which involves modifying the internal physical components of the system, and it can also be "soft-modded" using software to modify and expand its capabilities. Soft-modding allows you to add more channels, improve functionality and play backups of your games. You will need to use the WAD file format to install channels and you will need to use a specific WAD installer to uninstall the channels as well.
Download WAD Manager on your computer and place the contents of the .zip file on your SD card.
Open the HomeBrew channel on your soft-modded Wii. Select WAD Manager to load the application.
Select the location of the WAD file. You may be using the system's internal storage if the channel was originally installed there. You may also have it installed using the SD card or on a USB drive.
Press "A" and navigate to "uninstall WAD." Uninstalling the WAD will remove it from your system completely and delete the channels from your main menu. Do not use the Wii's built in channel manager because the title will still be listed on the system, while using WAD manager deletes the channel entirely.
Modifying your Wii is not illegal. It may void your warranty, though. It is illegal to download backups of games you do not personally own.