Note: This page is about the Firmware on your Wii and upgrading/downgrading it. For hacking any Wii, please refer to the USB Loader page.
Which Firmware is on my Wii?
On the channels page of your Wii, in the lower-left corner, is the Wii Options button. Click on it. Now click on Wii Settings. You will be presented with the Wii System Settings 1 page. In the upper-right corner is the current Wii Firmware you are running.
Which Firmware is most recommended?
At the moment, 4.1 is the most recommended firmware. The least recommended is 4.3 followed by 4.2, please don't use them. 4.2 and 4.3 did not add any positive capabilities to the system, only tactics for hindering homebrew (all of the 4.2 tactics have been bypassed at this point using methods described on the USB Loader page, whereas 4.3 is still being worked on).
4.2 is the same as 4.1 except that 4.2 added anti-piracy features. There is ZERO advantage to a 4.2 upgrade.
4.3 is the same as 4.2 with the addition of IOS58 (which you can install safely via DOP-Mii) for USB camera support. 4.3 also added a slew of more successful anti-piracy features. There is ZERO advantage to a 4.3 upgrade.
Firmware 4.1 is the same as 4.0 with only one difference. Firmware 4.1 includes a fix for a bug with Wii Sports Resort. That's it. There is no reason to be on 4.0 instead of 4.1. The better choice is 4.1, hands down.
All firmware is fully hackable, with varying degrees of issues. There is no need to remain on any firmware below 4.0. If you are on a firmware below 4.0, then you are missing out on SDHC support and the ability to store games and channels and launch them from an SD(HC) card.
For more detailed information on the differences between firmware/System Menu versions, review the System Menu page on WiiBrew.
How do I upgrade/downgrade my Firmware to 4.1(J/U/E)?
It's super easy with DOP-Mii. This is included in the WeHackWii Package.
If you have not yet installed the HomeBrew Channel, then you'll need to head over to the USB Loader page and learn how to hack your Wii. Once you are done with that guide, then come back here and follow the steps below to install the most recommended firmware 4.1 on your Wii system.
Is there an alternative upgrade/downgrade method?
Yes, you can use WAD Manager (which is included in the WeHackWii Package) to install the IOS37, IOS38, IOS60, BC, MIOS, and Wiisystemmenu (448 for NTSC-J, 449 for NTSC-U, or 450 for PAL) included with the WeHackWii Package. This will install 4.1, with the option for J/U/E up to you.
Launch WAD Manager from the HomeBrew Channel Install the .wad files listed in step 1
You can then use AnyTitleDeleter DB (which is included in the WeHackWii Package) to uninstall IOS30 (used by System Menu 3.0-3.3), IOS50 (used by System Menu 3.4), or IOS70 (used by System Menu 4.2) if you wish, and use DOP-Mii (which is included in the WeHackWii Package) to install IOS53, IOS55, and re-insert the Trucha Bug into IOS60 if you want to launch WiiWare from the SD card.
I'm on 4.3, is there anything I can do?
You can try using the Smash Stack or Indiana Pwns methods to launch DOP-Mii or WAD Manager and roll back according to the above methods. This may be risky and could brick you Wii, so we will not go into details at the moment. If you are competent enough to understand the first sentence of this paragraph and execute it yourself, please comment below about your experience. Otherwise, you should probably wait for more information and a more bullet-proof method.
Some people have had success with the Restore Your cIOS on 4.3 Wii guide. It follows the method mentioned in the above paragraph.
Here is a more detailed Indiana Pwns method guide: Wii Firmware 4.3 Downgrade _ Guide: Downgrade from 4.3 to 4.1.
There is also a 4.3 Virgin Softmod guide, but it is untested by the writers here.