It seems there is a single button allowed, and as long as you haven't exercised this privilege yet, you have the ability to select something brand-new. If you never chose a username to begin with, currently's your possibility to protect a better URL and e-mail compared to the arbitrarily generated number designated by default. Keep in mind, though, your old username/e-mail/URL will not work anymore when you choose the new one.
How I Change My Facebook Username
1. Start by clicking on the down arrow in the top right corner of the web page. Choose Settings from the drop down menu.
2. Under General Account Settings, you'll see the Username line. Click to Edit.
3. Enter your preferred username into the field provided. Facebook will let you recognize whether or not that username is available. Bear in mind, when you Set it for the first time, Facebook will let you alter it as soon as. You are also meant to use your genuine name when setting this.
4. Once you discover a Facebook username that is offered, click to save changes.
5. At this moment, your brand-new username is related to your Facebook profile and also active!
If you have your old URL connected to your site or e-mail signature, don't worry. All existing Facebook profile web links will be rerouted to your brand-new Facebook username.