Download forticlient SSL VPN from the below link:
http://www.iitk.ac.in/cc/vpn_update/sslvpn.htm
Extract the file and save to any location.
Now use this command
chmod +x forticlientsslvpn
If OS is 64-bit and application is 32-bit then run this command.
sudo apt-get install libgtk2.0-0:i386 libsm6:i386 libstdc++6:i386
now run the application.
sudo ./forticlientsslvpn