They have recently made the free name changes available.
...
For those who have been waiting: "Hell, it's about time."
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Free Name Change Now Available
by Blizzard Entertainment
// Nov 2, 2010 10:58:19 PM UTC
All StarCraft II accounts have been granted one free name change. If you'd like to change your character name, log in to Account Management and choose your StarCraft II: Wings of Liberty game license. On your game license screen a "Character Name Change" button at the bottom will initiate the request. After confirming that you'd like to change your character name, simply log in to StarCraft II and you'll be prompted to select a new one. Please be sure to use this name change wisely.
by Blizzard Entertainment
// Nov 2, 2010 10:58:19 PM UTC
All StarCraft II accounts have been granted one free name change. If you'd like to change your character name, log in to Account Management and choose your StarCraft II: Wings of Liberty game license. On your game license screen a "Character Name Change" button at the bottom will initiate the request. After confirming that you'd like to change your character name, simply log in to StarCraft II and you'll be prompted to select a new one. Please be sure to use this name change wisely.
Source: http://us.battle.net/sc2/en/blog/1050211#blog
-raindance and sacrificing your firstborn. If that sounds like too much effort, just use www.scmscx.com