What is my computer name?
Right-click on My Computer and select Properties. You should see the System Properties window; click on the Computer Name tab.
System Properties displays your computer name.
Your computer name is displayed (underlined in red above). Note that the trailing period is not part of the computer name.
To change your computer name, click the Change… button. Type a new name, click OK, and then click OK again on the System Properties window to save the change.
Macintosh OS X
Go to System Preferences (on the Apple menu) and click on Sharing.
The Sharing pane in System Preferences.
Your computer name is displayed at the top of the window. To change it, simply type a new name.