I wouldn't worry about it though. I think that pretty much most of ファンポップ would prefer a different ユーザー名 to the one they have now. I don't know that for a fact obviously, but I've come across a lot of peeople who want to change their username.
It's why so many people make new accounts, but I don't advise that あなた do that. Because you'll only lose everything you've done and have to start over. And tbh, no one's that bothered about your username.
No あなた can't change it. The only way to make a new ユーザー名 is to make another ファンポップ account. Now あなた can 削除 the one that あなた have, but that's something that あなた probably don't wanna do. If I were あなた I would.
