FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 197483

This article describes how to upgrade the VM license in order to use more vCPU and RAM.
Follow the link here below for VM license specifications:

The procedure includes the following steps:

1) Upgrade the VM license:

GUI: System -> FortiGuard -> FortiGate VM License
Click 'Upload' and click 'OK'

CLI: execute restore vmlicense <ftp | tftp> <VM license file name (path) on the remote server> < IP:port | IP > [ FTP username ]
# execute restore vmlicense tftp FGVM***********.lic
This operation will overwrite the current VM license!
Do you want to continue? (y/n)y

Please wait...

Connect to tftp server ...
Get VM license from tftp server OK.
VM license install succeeded. Rebooting firewall.
2) Shut down the VM
3) Upgrade the hardware
4) Start up the VM