How to legally change name?

I want to add James as a middle name. How do I go about this?How to legally change name?
If you are over 18, go to the courthouse and file the paperwork, if you are under 18, have your parents do it.How to legally change name?
see the first answer but you will have to run an add in the paper as well and prove you are not doing it to avoid a debt or other legal issues.

you can also do a dba or doing business as. that is also via a court.