Ok, I don't know how you could have missed this, but on the Edit Profile Page...
Quote:
Your login (user) name cannot be changed.
"Remember how much fun you had shooting spitwads at the teacher in seventh grade? Imagine applying that kind of attitude to actually [censored] with Mitsubishi!" - Jello Biafra
Deffy, he's asking about his PDN, not his Login name; and simply put, we don't allow PDNs (public displayed names) to be changed without one hell of a good reason as they have to be updated through the control panel.