Firmware Code And files

Sori bt i need help on several questions.............
1qt:why izzit that my phone cant go into 2g even though its fully unlocked and the netword mode appears.
2qt:what are the advantages and disadvantages of upgrading from 3.X to 4.X or 5.X.
3qt:where can i get this files and the program needed to upgrade.
4qt:i want to noe all kinds of formating hte phone and how to do it....
i have the griffin cable..your help would be valuable and btw this phone was bought from CPW uk n on 3 although its unlocked...thank u very much for your effort to look at this message