In order to reset the password for MediaWiki's admin, there are a couple of options:
1. The first and easiest one is to use the option 'E-mail new password' next to MediaWiki's login. In this case the password will be sent to the email address assigned to the administrative user for the MediaWiki installation;
If this does not work for you, there is a another way to reset MediaWiki's admin password.
2. Go to your cPanel > phpMyAdmin and select the MediaWiki database from the menu on the left. The page will refresh and the database tables will be displayed on it. Open the SQL tab (located at the top navigation bar).
In the text field write the following SQL query:
UPDATE user SET user_password = MD5( CONCAT( user_id, '-', MD5( 'NEWPASS' ) ) ) WHERE user_id =1
Then click on the GO button to submit the query. If everything goes fine without errors, you should be able to login to MediaWiki with the new password.
If you have problems with the above, try contacting your web host for assistance. You can always count on Siteground's Support for similar problems.