It has finally happened. Those of you who want to change your name in Minecraft now can. The only thing you need is a Mojang account. If you currently sign in to Minecraft with an email address, you’re all good! Otherwise, you can migrate your old Minecraft account here.
Just head on over to your Mojang account page and click "change" next to your username. You cannot steal somebody else name, the names are still unique. For you to take somebody else name you must wait, though. 37 days after they change their name, the old one will become available.
Mojang will be freeing up all those old unpaid usernames when the new name changing feature is released. After changing your name you have to wait 30 days before you can do it again.
Server owners need not worry, though. Banned, whitelisted and oped players will keep their status. They also keep their inventory, pets, statistics and everything they own on a server.