1. Log into mySQL and backup the SQL database.
2. Download the current wiki files with FTP
3. Download the latest version of MediaWiki
4. Move the folders "images" "extensions" and "skins" from the backup file of your current wiki to the folder containing the new version of MediaWiki.
5. Move the files "LocalSettings.php" and "AdminSettings.php" from the backup file of your current wiki to the folder containing the new version of MediaWiki.
6. Upload all the files from the folder containing the new version of MediaWiki and the items you moved into that folder via FTP to your wiki folder. Use replace all.
7. Open up terminal and type in: ssh -l username website.com
Note: Make sure there's an AdminSettings.php file in the wiki root, and it contains up to date information.
8. Navigate to the maintenance directory of the wiki and enter the update script: php update.php --aconf ../AdminSettings.php