Changing your Hostname without Rebooting in linux is a pretty basic task but if you are not too familiar with Linux, you can have difficulties.
Just follow the below steps and you will be fine :-
a) Log on as root and move to /etc/sysconfig and open the network file.
b) Update the file with your new hostname.
c) When you are done, save your changes and exit vi. Next we will edit the /etc/hosts file and set the new hostname.
d) Now use the hostname program to change the hostname that is currently set.
e) Finally, Restart the network to apply the changes we made to /etc/hosts and /etc/sysconfig/network.
Hope it helps!!