KuulKuum: my recollection is that PV550 and 900 Series A hardware, that was shipped from the factory with version 1.03 firmware, could only be upgraded as far as 1.07. The boards simply didn't have enough memory to run anything but v1.x firmware.
My recollection is that Series B and later hardware, even if it was shipped with v1.x, could be upgraded to v2, v3, and even v4 firmware.
But that's based on recollections from at least 25 years ago, and I could not find any confirming notes in the Knowledgebase. I'd say any PanelView 550 Series B terminal has already given the user a lengthy service life and should be a candidate for replacement instead of upgrade to support new features.
PanelView did a pretty good job of checking compatibility during download, so the risk of "bricking" a terminal is likely low.
I'll be interested to hear of the results.