You can do it like this: in the ISPConfig tarball, after you've unpacked it, there's a file httpd.conf_https. Copy it to /root/ispconfig/httpd/conf and rename it to httpd.conf (make a backup of the current httpd.conf before!). Then open the new httpd.conf and replace {SERVER_NAME} with the server name (have a look at the backed-up httpd.conf to find out the correct value).
Then open /home/admispconfig/ispconfig/lib/config.inc.php and change the ISPConfig URL from http to https.
Finally restart ISPConfig:
Code:
/etc/init.d/ispconfig_server restart