[CentOS] Really changing the hostname

I need to change the host name on a test server, and in the past when I 
used hostname to change the hostname, it did not seem to change it 
everywhere.

I really don't want to do a rebuild just yet, but I have to feel 
confident that hostname is really changed (reboot is not too much of an 
issue).

What is the recommened practice?  Other than get it right the first time.