Here is a guide that will show you how to change your computer name. If you want to change the name because you made a mistake in naming the system during the installation process (or any other reason) follow these steps:
First you need to change the hostname, to do this open a terminal window (press Superkey and type: terminal) and copy+paste the following line:
sudo gedit /etc/hostname
Now replace the current host name for the new host name, save and close the file.
Now you need to replace the current host name for the new one you used in the previous step. To open the hosts file copy+paste the following line:
sudo gedit /etc/hosts
And replace the system name after 127.0.1.1. When done save and close the hosts file and restart your computer. To check if it worked open a terminal window and the new computer name will be shown after yourusername@