Get an sd-card, then follow the 4.2 softmod guide below.
After your wii is softmodded you will download system menu 4.2u from NUSD and pack it as a wad.
(make sure you have bootmii and priiloader first)
You will load wadmanager, use ios249
Install ios70patched from the 4.2 guide first
2nd Install system menu 4.2u
The reinstall priiloader