If you don't want to reboot your computer, then become root and type this:
[arnav@dhcppc1 ~]$ hostname lappy

then exit your terminal and open a new terminal.

The actual file to change your hostname is:
[arnav@dhcppc1 ~]$ vi /etc/sysconfig/network

If you edited file /etc/sysconfig/network, then you need to reboot your
computer.