As you can read here, you'll be needing atleast 1000 posts in order to have your name changed (unless you decide to become a Donator).
Once you meet the requirements, you can request the namechange here.
Middleman since: April 13th, 2011
Marketplace minion since: April 18th, 2011
Runescape minion since: June 6th, 2011
Moderator since: September 28th, 2011
General Moderator since: November 2nd, 2011
Global Moderator since: April 29th, 2012
Super User since: November 1st, 2013