To remove Plesk from your server, follow these steps:
/usr/local/etc/rc.d/psa.sh stoppkg_delete `pkg_info | grep psa | awk '{print $1}' | xargs -n100`rm -rf /usr/local/psa/var/named/etc/namedb/named.conf, remove zone files from /var/named/etc/namedb/master/, and modify the file /etc/rc.conf appropriately. rm -rf /etc/psa