Your hostname or otherwise Computer Name is the name that your computer uses inside the network it is connected to in order to distinguish itself. Usually you setup your own during the setup of the Operating System but if for any reason you want to change it check out the guide below.
Open a terminal
CRTL + ALT + T
sudo vim /etc/hostname
Change it to whatever you want your name to be, Save and Close the file
Now we have to update our hosts file in order to route ourselves.
sudo vim /etc/hosts
Find the line where it says: 127.0.1.1 usernameHere and change it to what you entered above and then Save and Close the file.
Enjoy your new Computer Name :)