Visit your user profile page to edit your user and display name.
When you’re logged in, you can click to edit the fields in your profile.
Here’s a copy of our in-app announcement:
What’s in a @name?
That which we call a @user
Or any other w0rd if spelled in l33t;
So @user would, were she not @user call’d,
Retain that dear perfection which she owes
Without that title. @User, doff thy name,
And for that name which is no part of thee
rename thyself.
(You can now edit your @user and display names. 
)