How to change a username (zoho.loginuser)

Hi,

Is there a way to change a username (zoho.loginuser) and keep the same email (zoho.loginuserid) ?

I asked my user to change his Nickname in his User Account but it doesn't seem to work.

He still have the old username in the upper right corner. In Deluge, I have also the old zoho.loginuser.

Do I have to close the account and open a new one ? If yes, will I be able to open an account with the closed account email ?

Thanks,

Pascal