The hostname on the Parallels Plesk Panel server should be changed through GUI on the page Server->Server preferences for version 8.x, or on Settings -> Server settings for version 9.x, with the "Full hostname" field. Fill in the new hostname and click OK.
Parallels Plesk Panel will update its database and all needed configuration files such as /etc/hosts, /etc/sysconfig/network, /var/qmail/control/me, etc.
