Possible to upgrade without using itunes

Is it possible to download something like a dmg and somehow install this rather than using itunes? Three times I have tried and every time it gets a third of the way through and gives up. I hoping I could use the bandwidth at work to bypass the fact that itunes is trying to download a 1.1 GB lump which will kill my wireless download limit.

I found this link http://osxdaily.com/2012/09/19/ios-6-ipsw-direct-download-links/

But I think the links for the iPad 3 GSM & CDMA are the wrong way around. In Australia we don't have a CDMA network as far as I know but the file that was being created by the download appears to be the CDMA link.