ios 6 updated iphone doesn't work on my mac

I am currently using iphone 4 - recently upgraded to IOS 6,

and it doesn't work on my mac - a version of MAC OS X 10.5.8. - when it connects to itunes - which i have a latest version upgraded on my mac.

I tried to upgrade the Mac software of 10.6 and later versions to the latest versions, but i can't download them.

That's why I can't use itunes to upload the songs in my iphone, which is my biggest concern right at the moment.

Let me know how I can upload the songs in my iphone!