-Go to your Utilities folder (it is inside your Applications folder)
-Find and double click the NetInfo Manager
-Click the lock at the left-down of the window
-At the middle-top column where it says Directory Browser select the "users" and then from the column at the right select the name of the user that you want to change his/her name
-Under columns you can read MANY data about that user: Find the one that says at the left side "name" and double click at the right of it where you must by now reading the name you gave before
-Change it at whatever you like but keep it at no more than 8 characters
-Close NetInfo Manager and at the question of Saving Changes or Not, select Save
-Log out or Restart and everything sould be fine!
NOTE: If the above seem difficult don't try them but as long as you know what are you doing and don't mess with ANYTHING else then you sould be fine... However, if someone else will tell you another way to do this task then if you like, post it here so that we, the other members, will be able to get some extra knowledge
