Changing login screen info

I recently bought an iMAC that had been initialized and software, other than 'from the factory', had been installed. The Screen says "Mac OS X" and right underneath it "Mac Users Macbook Pro". Then the user name and password.
I want to change the "Mac Users Macbook Pro" entry for something more personal for me. Does anyone have any idea how to change "Mac Users Macbook Pro"?
Thanks,
VB Blue

System Preferences > Sharing > Computer Name > Edit

Then you can call the computer whatever you want, its usually automatically named by whatever name you put in when setting it up as your own and the model it is eg:

SlickShoes iMac