This article describes how to upgrade or downgrade firmware in FortiOS 7.2.
1) Login to FortiGate GUI.
2)Go to System -> Fabric Management.
3)Select the FortiGate and click upgrade.
4)To upgrade the firmware, select the firmware from tab "Latest" or "All Upgrades".
5)To downgrade the firmware, select the firmware from tab 'All Downgrades'.
6) Get the firmware downloaded from https://support.fortinet.com, go to 'File Upload' tab to upload the firmware.