First, login using the terminal icon on the Untangle box itself and set your root password.

Next enable SSH to start at startup:
rm /etc/ssh/sshd_not_to_be_run (you can disable it later by entering touch /etc/ssh/sshd_not_to_be_run)

Now run it:
/etc/init.d/ssh start

Now edit the file /etc/ssh/sshd_conf (using vi or similar) and change the Port to something other than 22 (say port 1022).

Next you need to go to the web interface and enable Port 1022 for internal traffic under the packet filter - this can be found under Config -> Networking -> Advanced.

That should be it.