PanelBuilder32 software only goes up to 3.8x.
But PanelView terminal firmware goes to version 4.x.
RA doesn't distribute the firmware files separately from PanelBuilder32 software; the firmware upgrade utility is included on the CD as are all the firmware files.
There are actually two different firmware files you could use; one is for downloading via the network port, and the other for loading via the PCMCIA flash memory card.
Edit: I checked my installation of PanelBuilder32, which came via Web download, and sure enough the firmware utility and firmware files aren't there. They must be only on the physical CD.