How do I download updates on iphone 3.G?

I have had iphone 3 for over a year but have never downloaded itunes or any app. I now want to download scriptures, but it tells me I need a 3.0 update. When I press the app button and press the upgrade arrow, it says no upgrade. yet if I try to download the scriptures, it says I must get the 3,0 upgrade. I don't know how to do that. I basically use the email , cell phone and the address book. I do not use text . How do I get the iphone updated with usual upgrades and then get the download for scriptures? I know which scripture application I want and it is free. But I can't get it. I have never called about the phone and don't know how to download itunes either, but right now the scriptures are my main concern, and getting proper upgrades if changes have been made to this 3.G version. I am not yet ready for 4.0 version. I sure hope someone can help.