[Centos] Have question about centOS-3.3

I am currently running centOS-3.1.

I have not received any package updates since Sept 1.

Is this in part due to creating new isos which would be named centOS-3.3.

How would I go about updating my system from centOS-3.1 to centOS-3.3,
or would I even need to and just keep downloading updates like i do now.

My system is running very smoothly with no errors or issues,
I was just wondering why there hasnt been any package updates available.

Would it be necessary to download the new isos and upgrade my system?
Will the package updates be available still for centOS-3.1.