If you are not satisfied with your selected facebook username or facebook profile URL then there is a good news for you. Facebook is giving you one more chance to finalise your facebook username. Once you change your facebook username you can’t switch back to the previous one, so make changes carefully.
Here is what you have to do to change your facebook username: Click on the “Settings” tab and you will find a “Username” tab there. Now click on “change” to select new username, check its availibility and if its available you can get that username instantly.
Shahab khan is a Tech blogger from India & a founder of VirginTech. He blogs about Technology, internet, Social media, computer tips & tricks and Web 2.0. 
{ 3 comments… read them below or add one }
Hi guys! I tried to change my facebook user name by i can not insert my desired name. Any solutions!!!
Hello Asif!
Actually facebook allows you to change your username only once. So you must have changed your username earlier before that’s why its not allowing you to do it again.
YEAH you are right