No matter what type of your HelpWiki system is, user cannot change their username.

If your system is an Application Help System, admin user can change their password in user profile,

If your system is a Knowledge Based System, user do not have rights to change or reset the password of HelpWiki system directly. The HelpWiki password will be always as same as your Windows password. That means if your want to change your HelpWiki password, you must go to change your Windows password first, then you can use the new Windows password to log in the HelpWiki system