User name

Hello
I'm a mother of a teen gamer. He was having issues signing into his acct a couple of years ago so I created an acct just to see if it would work. It did. Problem is the username. When I created the acct I had no idea people would see the name I created. Now my teen son has to game under a username with the word mommy in it. ( Lmao )
Is there anyway he can change the username without losing all the stuff he has saved in his acct ?
Its embarrassing for him to play in the community with this current username but he doesn't want to lose everything and start fresh with a new acct .
I'm not tech savy so please try to reply in simple terms .
Thank you very much!
- someone's mom