How to Change Your Computer Name on Mac OS X
 

When you’re sharing stuff back and forth between your computers, the names of those computers actually start to matter — in my case, I upgraded to a new MacBook Air because my old one has a dead screen and is out of warranty, so I made it into a desktop with an external monitor. That’s when I got an error that my two Macs had the same name. Oops! Luckily it’s an extremely easy fix.

http://www.howtogeek.com/tips/how-to...e-on-mac-os-x/