First, you didn't explain if you wanted to update the console itself (legit software), or the hack (homebrew, etc.)
Maybe you want to update the hack, for example, you have an old version of The Homebrew Channel ?
but you didn't provide any information about your current state or what you wanted.
You should tell which version you are on. Maybe you are on the latest "system menu" version already
(or use modmii like suggested above and it will overwrite all you have already)
Second :
There is no real "update" on Wii.
The "system menu" version is not the Wii firmware. It's just the version of the system menu.
Its internal files have also their own versions, and can be updated individually, with NO issue on other things. For example, having an updated file or not will not break playing old games which only look at old files.
Third :
Do you intent to play with legit disc, or backups over USB and homebrew ?
If you want to play a recent game (from disc) officially, it will contain the required files on the disc (on its partition update), and will ask you to update or install the missing files before launching.
Of course, agreeing could break your current hack if too old. again, you didn't provide any numbers.
What I'd suggest :
don't update. try, it works ! If the game works, good. if the game asks you to update, and you are not sure we will help you.
Homebrew don't rely on "system menu version". I'm still using 3.2E on mine, and everything works.
So, if you plan to play from USB loaders, or any homebrew, just try too see if it works. no need to fix what's not broken.
