Hi Azhar,
It depends on the business how they want to do. If the end users have to maintain the data or the administrator has to maintain the data.
If you want to allow the end users to maintain their user account details, then you need to change the settings in SCUM transaction. If you want to allow the administrator to maintain the data, then he can maintain the same for the users from the CUA system.
Regards,
Laxman