Use the graceful upgrade information or other firmware upgrade information in these release notes to upgrade your FortiGate-6000 or 7000 system to the latest firmware version with only minimal traffic disruption and to maintain your configuration.
You can also refer to the Upgrade Path Tool (https://docs.fortinet.com/upgrade-tool) in the Fortinet documentation library to find supported upgrade paths for all FortiGate models and firmware versions.
A similar upgrade path tool is also available from Fortinet Support: https://support.fortinet.com.
In some cases, these upgrade path tools may recommend slightly different upgrade paths. If that occurs, the paths provided by both tools are supported and you can use either one.
You can find the FortiGate-6000 and 7000 for FortiOS 6.0.15 firmware images on the Fortinet Support Download Firmware Images page by selecting the FortiGate-6K7K product.