Why can't I update my iTunes?

The "Apple Software Update" pop-up box comes up and every time i click "install" and then "agree"… The box just keeps coming up. I downloaded the newest Adobe update. I have an iPhone 5 and now I can't put music on from my laptop… Please Help! I've had the same iTunes for years… It say that it is version 2.1.3

Download it directly from apple.com, instead of using the update thing.

The current version of iTunes is version 11. You're so out of date that it's probable that your OS is too old to support the current version. What version of Mac OS are you running? ITunes 11 requires at least 10.6.8. If you're still running 10.4 or 10.5 then you need to upgrade your OS if your Mac supports it.