If you need to edit user information, go to Management > Users in menu bar. As the admin user you should see this menu and be able to edit the information.
Activate the line you want to edit by clicking it. You get to see the view "Edit user information". On this page you can edit the user information (name, email address), attach user to different sites in your domain tree, change the user's user group, set the default language and activate or deactivate the user name.