If you want to disable the option for your MediaWiki visitors to register accounts at your MediaWiki website you will have to add the following line in the LocalSettings.php file:

 $wgGroupPermissions['*']['createaccount'] = false;

You can find below detailed instructions on how to do this on your web hosting account using cPanel:

1. Go to your cPanel. .

2. Click on the File Manager icon

3. Click on the folder icon next public_html folder name

4. Click on the folder icon next to the folder in which your MediaWiki is installed

5. Click on the LocalSettings.php file

6. In the upper right corner you will see several management options for LocalSettings.php file. Click on Edit File

7. Look for a line that starts with $wgGroupPermissions. If there is no such line you should add it yourself and if there already is such a line you should edit it to look this way

$wgGroupPermissions['*']['createaccount'] = false;

 
8. Save the edited LocalSettings.php file and the new users account creation will be disabled.

If you have problems disabling the MediaWiki registration yourself, ask your host for assistance. SiteGround provides the best MediaWiki hosting and such requests are handled with ease.