If you have download the Build 12 full installer, you should simply let it extract on top of your current installation. There is a b12.exe and b12update.exe program file in the "Updates" folder, but you don't need these. They don't work anyway, because the original online installer server is down. But that doesn't matter, because you don't need them.
"Delocalizing" means moving all files from the ENGLISH subfolders into their main folders. Or, if you use a Russian version, from the RUSSIAN folder into their main folders. This is required, because then the game can find the files it needs. However, US versions are already delocalized by default, so the batch file doesn't have to do anything anymore. This doesn't matter either, because whether it delocalizes the files or doesn't have to because they're already delocalized doesn't make a difference; the end result is the same.