Documenting the key aspects
Before you can start the upgrade procedure, you should first take some time to document the key aspects of the network surrounding the firewall or Panorama. This information will need to go into a test plan that you can execute immediately after you have performed the upgrade as you will need to quickly ascertain whether the device is up and running and passing traffic as expected. It is important to identify key production applications and if possible, identify personnel who can assist in testing application functionality post-upgrade.
It may be prudent to make an upgrade checklist so that you don't forget any important caveats, as well as a contingency plan in case something goes wrong, which includes at which point fallback is required. Set this point so that you have plenty of time to troubleshoot for minor oversights, but not so long that it impacts the business. Arrange for an appropriately sized maintenance window beforehand. Here's...