From your GitHub home page, select the drop-down menu on the right and select Settings.

Next, click Account from the options in the sidebar on the left.

Hit change username to start the process.

Click the big red button to acknowledge you understand the risks.

Maybe you don't like your current GitHub username, or you just want to change it. Fortunately, changing your GitHub username is very easy. Beware, as changing your username can have unintended side effects like missing redirects for your old profile and repositories.