To change the CentOS host name you should edit:
/etc/sysconfig/network

You can use your favorite editor (like vi)
vi /etc/sysconfig/network

* i prefer mcedit

Change Hostname: (replace 01.direkthost.net with your own hostname)
HOSTNAME=01.direkthost.net

Also edit, and add your own hostname:
/etc/hosts

Restart your network  (CentOS 6 / CentOS 7)
/etc/init.d/network restart
systemctl restart network