Add the following to your theme’s function.php. Default values are shown below, except changing ‘number’ from 45 to 15. Only the changed values need to be included, so you can either leave the default values or remove/comment out those lines.
wordpress tutorial
As you may know, in a default Joomla installation, new users can register for your site and then get immediate approval as ‘registered users.’ Or, you can set it so Joomla sends the new user an email with a “click on this link to confirm” in order to make sure that they have entered a valid email address.