From what I can see, my Chinese iPhone4 does not accommodate iTunes
What is wrong with you China?!
I'm sorry but I don't understand what you mean
On your phone click Settings, then go to General, then Software Update. This should then search for the latest version of iOS which will be 6. You'll need to be on WiFi though.
Otherwise iTunes is already on the phone as an app - but it's for downloading music / podcasts e.t.c
To download the software on your computer (iOS 6 I mean) then you'll need to download the full iTunes to your computer and do it that way.