N600 and change first name

[immihelp]

I have naturalized to U.S.A citizen with N-400 in last year 2010 and intend to apply for Citizenship application for my 18yrs old son who is living with me from 1998 in U.S.A. and he has Green card since 2005.
Please advise whether N-600 is the right process for my son case.
Also, please advise when can change his first name because current his first name is difficult to make sound for his American friends? before or after or during N-600 process?

[immihelp]

You can do the name change either before or after.