Don't update. You will lose preloader and the best method of removing the wad that caused your banner brick.
If you can find the wad you installed usb loader with and put it on your SD card it will be very easy to remove it and get your Wii back healthy again. If not you can use anytitledeleter to remove it, but be careful as you can remove critical files and render your Wii totally black screen full bricked.
Let us know how you get on, don't try stuff without asking first to be safe.