Hello and Welcome to LinuxQuestions,
Depending on what distro you use there are some places where hostname is/can be set. Manually you just use the command
log out and it's changed for the duration of the session. If you want to make it permanent change the hostname in whatever file it's used (/etc/hostname, /etc/hosts, /etc/sysconfig/network, ...) depending on your distro. If you indicate what distro you're using, better help can be offered. The more information you provide the more detailed answer you'll get. Have fun with Linux.