Assuming you're speaking about pagure.io or src.fedoraproject.org, you can change your full name but not your username. This one is coming from FAS and sync when logging in.

Yes for the username!

Any suggestions for that?

It's not possible and won't be :)

To be a little more helpful, the only way you could change username is by creating a new account in fas. Then log out from your current account and log in with the new one.
Then you'll have to convince all the projects you are a member of to add you under that new username.