Changing userName

How can I change my username's shape?

arminsong to ArminSong

You can try sending feedback, because it is only a minor change they might consider it. Don't get your hopes up though, I'm not sure if they do these kind of things. I haven't tried changing my name from yashin to Yashin because I just don't care 🙂

Yashin

Your username is final once you created it on this site.
It should have warned you of this when you created it.
I remember seeing the warning when I created mine.
Like the poster above stated you can always try by sending feedback and asking. But I wouldn't hold your breath.
The send feedback link is at the bottom of any and every RHP page under "Support". Good luck.