Officially there is only a generic tar.gz package available. As I use Ubuntu most the time, I decided to build .deb packages for 32/64bit Ubuntu with a nice desktop icon to start : )
This packages should also work on debian, but i did not test this on myself now (will follow).
For upgrades just download the new package and install it, the package manager will do the upgrade for you.
I will share my packages here for you to download:
Update 10.3.2017 (build on Ubuntu 16.04):
Since version 4.4.2327-2 builds are generated on Ubuntu 16.04.
Old versions (build on Ubuntu 16.04):
Old versions (build on Ubuntu 14.04):
Legacy version (works with Ubuntu < 15.04):
Forticlient SSLVPN 4.4.2303 32bit
Forticlient SSLVPN 4.4.2303 64bit