Backupand format your sd-card
Extract cIOS60-v6174.zip to sd:\wad
Extract (4.1u)-System Menu-NUS-v449.zip to sd:\wad
or perhaps (4.1e)-System Menu-NUS-v450.zip
Boot the wii, wadmanager starts
Select ios249, press A
Install SM 4.1 for your region. E = pal, europe. U = NTSC, usa
You'll need a gc-controller to do this.
If you don't have a gc-controller, you can restore your nand, but you'll lose everything you installed after the backup. Save games, hacks, etc.
Extract Bootmii-KEYFIX.rar to sd:\
Restore your nand.