Help... I cant update my Os

Depending on which Mac you have you may have three choices to upgrade to: 10.7 Lion, 10.8 Mavericks (both paid for upgrades) or 10.9 Mavericks (free). Upgrading to any one of them may render some of your older applications unusable as none of the upgrades support Rosetta which enabled older PowerPC apps to run, so it's worth checking for compatibility problems before upgrading:

http://roaringapps.com/apps?index=a

Also, before upgrading, make sure you have enough RAM for the new OS to run efficiently. They all state that 2gb is required, although 4gb or more would offer a much better user experience:

http://store.apple.com/us/product/D6106Z/A/os-x-lion

http://store.apple.com/us/product/D6377Z/A/os-x-mountain-lion

Mavericks is available directly from the Mac App Store in the Apple Menu.

Before upgrading ensure that you have tried and tested backup that you can restore from should you need to for any reason.

I have tired software updates and install them all and also tried downloading OS 10.7.4 and i wont let me update as i dont have 10.7

That's because Lion is not an update from 10.6.8, it's a paid upgrade from the App Store. You'll need a special code to buy it, as it now over 2 years old.

http://store.apple.com/us/product/D6106Z/A/os-x-lion