Do I have to re-register a new Facebook account to change my facebook.com/USERNAME?
Or are there any ways to change it?
You can only change your Facebook username once. If you have already changed it then there is no way to change it again. You would have to setup a new account and claim a new username that way.
The option to change your username is in
You can only change your Facebook username once. It seems that you have done it already.
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