http://www.fortivoice.com/sites/default/files/productdatasheets/Management_software_download_instructions.pdf
Before you being you should backup the configuration (File --> Save to --> File).
You can also copy the "LastSaveConfig.tsd" from here:
C:\Program Files (x86)\Fortinet\FortiVoice Management #.##
To update the current software version run the downloaded .EXE file and follow the on-screen installation instructions. Once, you have installed the new management software, run the application and click on "Configure Auto-Detected system". The new software will detect that there is an older version of the firmware running on the software. This will cause the software to prompt you to update the system. Again, follow the on screen instructions to update the system firmware.