You can "safely" upgrade the FortiOS directly to the target firmware code if it's brand new and since it still has a default configuration. You only follow the upgrade path if there's an existing configuration and the upgrade process will handle the changes in the command line or features (if there's any).
I upgraded a brand new standalone FortiGate and it was shipped with a default 6.4 firmware.
FortiGate-xxF login: admin
Password:
You are forced to change your password. Please input a new password.
New Password:
Confirm Password:
Welcome!
FortiGate-xxF # get system status
Version: FortiGate-xxF v6.4.4,build5543,201214 (GA)
Firmware Signature: certified
Virus-DB: 1.00000(2018-04-09 18:07)
Extended DB: 1.00000(2018-04-09 18:07)
IPS-DB: 6.00741(2015-12-01 02:30)
IPS-ETDB: 6.00741(2015-12-01 02:30)
APP-DB: 6.00741(2015-12-01 02:30)
INDUSTRIAL-DB: 6.00741(2015-12-01 02:30)
Serial-Number: FGxxFT923901234
IPS Malicious URL Database: 1.00001(2015-01-01 01:01)
BIOS version: 05000011
System Part-Number: P25132-01
Log hard disk: Available
Hostname: FortiGate-xxF
Private Encryption: Disable
Operation Mode: NAT
Current virtual domain: root
Max number of virtual domains: 10
Virtual domains status: 1 in NAT mode, 0 in TP mode
Virtual domain configuration: disable
FIPS-CC mode: disable
Current HA mode: standalone
Branch point: 1803
Release Version Information: GA
FortiOS x86-64: Yes
I uploaded the target firmware and the direct upgrade only took around 4 minutes to complete. I proceeded with the configuration afterwards.
FortiGate-xxF # get system status
Version: FortiGate-xxF v7.xx,buildxx (GA.M)
Security Level: 2
Firmware Signature: certified
Virus-DB: 1.00000(2018-04-09 18:07)
Extended DB: 1.00000(2018-04-09 18:07)
AV AI/ML Model: 0.00000(2001-01-01 00:00)
IPS-DB: 6.00741(2015-12-01 02:30)
IPS-ETDB: 6.00741(2015-12-01 02:30)
APP-DB: 6.00741(2015-12-01 02:30)
FMWP-DB: 0.00000(2001-01-01 00:00)
INDUSTRIAL-DB: 6.00741(2015-12-01 02:30)
IPS Malicious URL Database: 1.00001(2015-01-01 01:01)
IoT-Detect: 0.00000(2022-08-17 17:31)
Serial-Number: FGxxFT923901234
BIOS version: 05000011
System Part-Number: P25132-01
Log hard disk: Available
Hostname: FortiGate-xxF
Private Encryption: Disable
Operation Mode: NAT
Current virtual domain: root
Max number of virtual domains: 10
Virtual domains status: 1 in NAT mode, 0 in TP mode
Virtual domain configuration: disable
FIPS-CC mode: disable
Current HA mode: standalone
Branch point: 1706
Release Version Information: GA
FortiOS x86-64: Yes
System time: Mon Oct 7 03:14:05 2024
Last reboot reason: warm reboot
