which menu are you on? 4.1? 4.2? 3.4? if you are on 4.x then you can run the bannerbomb for 4.2 from the SD card icon in the main menu
otherwise you will need to get the bannerbomb that works on 3.x and that one can be loaded from the channels / SD card tab.
Just google on bannerbomb and you will find it. It is pretty easy to run
And do make sure you make a bootmii backup of your nand asap as it can save your wii incase of a brick...