Controlled upgrade
Using a controlled upgrade, you can upload a new version of the FortiOS firmware to a separate partition in the FortiGate memory for later upgrade. The FortiGate unit can be configured so that when it is rebooted, it will automatically load the new firmware. Using this option, you can stage multiple FortiGate units to upgrade simultaneously using FortiManager or a script.
To load the firmware for later installation:
execute restore secondary-image {ftp | tftp | usb} <filename_str>
To set the FortiGate unit so that when it reboots, the new firmware is loaded:
execute set-next-reboot {primary | secondary}
where {primary | secondary} is the partition with the preloaded firmware.