Chapter 10 Install and System Administration for FortiOS 5.0 : Basic Administration : Passwords : Lost Passwords
  
Lost Passwords
If an administrator password has been lost, refer to the SysAdmin’s Notebook article “Resetting a lost admin password,” found at docs.fortinet.com/p/sysadmin-s-notebook-and-tech-notes.
See Also
Passwords
Password considerations
Password policy