Use Wii Duplicated Channel Remover from Waninkoko to delete the duplicated versions of the Weather and News Channels, respectively. Then, use Firmware Downgrader v1.11 to upgrade to 4.0U, or use NUS Downloader to download the WADs of the IOS 60 v6174 (not the v6400. That's a stub, and you won't be able to run any code from it. If you install it, you'll get a brick) and the v417 of the System Menu. The rest is simple: use WAD Manager to install the WAD's.
Regarding the steps, well, I don't think I can explain them better (my english is very limitated, as you can see)... If you find it difficult, use the Firmware Downgrader. It's the most simple way to upgrade.
EDIT: however, just as SifJar says, I don't see any reason to update to 4.0U. You can update to 4.1U, it's the same thing. The only difference is that it has a bugfix.
To 4.2U, do you mean? DON'T DO IT. You'll obtain the brick-like error 003 upon booting, because your console is a Korean one.
EDIT: LOL, it seems I misunderstanded you. Well, yeah, you can update to 4.1U doing the same proccess. However, I think the Firmware Downgrader MOD from Attila is the only one that includes the 4.1X and 4.2X firmwares.