Mojang will now allow you to change your Minecraft name. This new capability went live today. You can change your name by visiting your Mojang account page.
With the name change capability, there are still a few rules in play – names have to be unique and you can only change your name every 30 days, even to change it back.
You can change the capitalization of your name while bans, whitelists, and inventory will persist for players even if they change their names.
You can read through the other FAQ about the change on Mojang’s announcement.