Handheld Upgrades?

I have a HP Jornada 540 Series (2000 yr release) with Microsoft Windows CE, Ver 3.0.9348 (build 9357). I would like to upgrade the operating system to Windows Pocket PC 2003,so as to take advantage of the latest software. Is this possible, and how do I go about it?
Microsoft advised me to contact HP, assuring me it was. However, HP said it was not. But, was it just their sales dept answering out of ignorance. I would appreciate any offers of help concerning this issue. Surely, once these devices are a few years old, you’re not obliged to throw them in the bin?
Kind Regards,
Mike.