First let me tell you that most likely you will brick your wii if you update it, thus making it worthless. But if you go to the main page at
You can safely update your wii to 4.0 using this I have done it, though I really don't think you gain anything with it being updated.
Please make sure to have a preloader on your will this way if an issue happens you can save your wii from being bricked. You can find
a preloader on the main page.