iPhone 4 (not 4S) and iOS - please help!

I am still using the iPhone 4 and wont be upgrading for another few months. I have never had any version iOS on the phone...I cannot get it on.

I have tried following the Apple instructions - Settings > General > Software..... but my phone does not have a Software option to select.

It has been months since I've been able to download a new app, or update existing ones, because everything needs iOS - and now the existing ones are giving me pop up messages saying they are about to stop working unless I update the app....which I would LOVE to do, but can't.

Can someone please tell me how to get iOS on the iPhone 4....or if it's not possible, just let me know that so I can stop trying - it's driving me crazy!!

Thanks