With the PanelView 550, it's possible that the terminals are too old to support firmware upgrades. About two years worth of the early production in 1993-1994 used a memory chip that was too small to hold later firmware footprints.
If the terminals are version 3.0 or later firmware, they support both flash firmware updates and PCMCIA ATA Flash memory cards, so performing an upgrade is particularly simple. Version 2.x firmware will require some different tools.
Post more information about the terminals (either off the label on the back or from the configuration screens) and folks can tell you more.
PanelView firmware is included on the PanelBuilder32 CD and is available for download. It's always a good idea to have a support contract when you're looking for upgrades and enhancements.