@stephenw10 Since my router is functioning normally in all other regards I'm not that concern at this time. I will become familiar with the console interface and attempt to identify the differences in my configuration before/after the upgrade and post results here.
My configuration only runs two additional services: pfBlockerNG and UPS.
My procedure was:
Shutdown the system from the GUI menu.
After confirming the system was shutdown, pulled power.
Pulled the USB from UPS and replace batteries. Note: intent was to do UPS maintenance as well and did not want a forced shutdown by UPS during upgrade.
Restarted firewall, confirmed all services were working sans UPS (USB still unplugged).
Made configuration backup.
Performed an upgrade from GUI.
After device restarted and after 10-15 minutes of no response from GUI -- realization that GUI access was blocked; however, firewall was allowing inbound/outbound traffic as expected.