Set or Change Hostname (via the GUI)

• Open System Preferences
• Select Sharing
  Select the Edit button and enter your desired Local Hostname and click OK
  

...

To permanently change the Hostname of your device via the terminal

Set or Change Hostname (via Terminal) - OS X

...

10.6 - 10.10

• Open Terminal by going to Applications, then Utilities, and select Terminal

• The type the following:

sudo hostnamescutil –-sset HostName new_hostname
For example:  sudo hostnamescutil –-sset HostName ECE-MAC

Set or Change Hostname (via Terminal) - OS X 10.6 - 10.8

• Open Terminal by going to Applications, then Utilities, and select Terminal

• The type the following:

...

Note:  It may also be necessary to perform the following commands to solidify the changes

sudo scutil --set ComputerName <hostname>
For example: sudo scutil --set ComputerName ECE-MAC
sudo scutil --set LocalHostName <hostname>
For example: sudo scutil –--set HostNameLocalHostName ECE-MAC