Suspend the active firewall to trigger a failover to the passive firewall. With traffic now running on the former passive unit, upgrade the suspended (now passive) firewall and confirm proper operation. Then fail traffic back and upgrade the remaining firewall.

Shut down the currently active firewall and upgrade it offline, allowing the passive firewall to handle all traffic. Once the active firewall finishes upgrading, bring it back online and rejoin the HA cluster. Finally, upgrade the passive firewall while the newly upgraded unit remains active.

Isolate both firewalls from the production environment and upgrade them in a separate, offline setup. Reconnect them only after validating the new software version, resuming HA functionality once both units are fully upgraded and tested.

Push the new PAN-OS version simultaneously to both firewalls, having them upgrade and reboot in parallel. Rely on automated HA reconvergence to restore normal operations without manually failing over traffic.