How do I rename my mac

[Bulldog VII]

Hi all

I've just noticed that I have spelt my name wrong when I set my mac up. I have no idea how to change it, when the screen saver comes on it is almost my name there as JOHN DOE's MAC

I know I'm not too good with these things!

 

[Tallest Skil]

System Preferences, Sharing. Rename from there.