All you need to do is to edit the file /etc/motd
- Ssh into your server
- nano  /etc/motd  (if nano is not installed just type "yum install nano" and then rerun the command nano  /etc/motd )
- change it to whatever you want
- Press CTRL+X, you'll be asked if you want to save the file. Type y and hit Enter
All done :)
