You can't change name through the forum edit profile, that's why i suggest you try through your Arturia account.
In your Arturia account you have e-mail, your real name, and also a "Display Name".
Is the name i can see here in this user forum, the name you have put in the text field "Display Name" on your "My Arturia" account?
If you can't change the name for the forum through your Arturia accounts "Display Name" text field, when you are in edit mode for your Arturia account profile, then i suggest you contact Arturia support through your Arturia account.