Upgrade Question

The most recent version of Flash I own is MX 2004… is there a way to “upgrade” to the most recent version, or would I have to buy the full CS4 version outright?

If there is no upgrade, can I still make usable swfs with Flash MX 2004? It’s been a few years since I used the software, not sure where the technology is at these days…

Thanks for the help!