MediaWIKI Upgrade
There are all sorts of tutorials on upgrading MediaWiki. Here's the "down and dirty" version.
BACKUP!
Don't take a chance that the upgrade will mess something up. Make a backup. For MediaWiki, that consists of two items: The website files and the data base.
Backup the website files (actually make a copy)
mv WebSiteDirectory WebSiteDirectory.VERSION-WORKING (my naming convention)
The above is the quickest way to make an exact copy of the website files (unlike NTFS, Linux permissions are simple and will be copied with the above command) and also test as you go. IE, the copied files can be checked for functionality by going to the web site.
Install
Get the latest version (FULL version, not upgrade) of MediaWiki:https://www.mediawiki.org/wiki/Download
Unpack the TAR File: tar -xvzf mediawiki-1.xy.0.tar.gz -C /var/www/html/WhatEverDirectory (Don't worry about making a mess with a lot of files as the TAR File's first item is a Directory, as it should be)
Rename it to the original WebSiteDirectory (as that Directory name was changed): mv mediawiki-1.xy.0 WebSiteDirectory
Set the proper file permissions for Apache (adjust as necessary for your environment);
chown -R apache:apache /var/www/html/WhatEverDirectory
find /var/www/html/WhatEverDirectory -type d -exec chmod 755 {} \;
find /var/www/html/WhatEverDirectory -type f -exec chmod 644 {} \;
find /var/www/html/WhatEverDirectory/images -type d -exec chmod 755 {} \;
Copy previous version of MediaWiki website files into the new directory: cp -R -n -v WhatEverSource WhatEverDestination (This will not overwrite any new files, IE "upgraded" files, but has the effect of copying all the extensions, images, and any other files from the old website version, while paying deference to the newer files. Of course if any MediaWiki code files have been modified, the same modifications should be made to the new files, but this is rare.)
Upgrade extensions (if there are upgrades). Visual Editor is one that needs to be kept up. Hopefully nothing breaks for extensions that don't have upgrades available.