Get a hold of Bushings Recovery Disc. You can find that over at Hackmii.com (Browse the archives). Make sure you get the proper one for your region.
Then, using wiiscrubber, extract the ios30.wad and the systemmenu.wad (not the exact names, but you'll recognise them)
Copy both wads in the wad folder in the root of your sd card.
Launch WadManager 1.3 from the hbc (or other means of launching hombrew)
First install the ios30.wad, second install the systemmenu.wad.
Exit WadManager. You are now on 3.2