I propose following procedure: create a copy of your Wiki-database, download
the new version into a seperate folder of your webserver (don't forget all
the extensions you are using in your Wiki). Copy the image-folder into your
new Wiki. Copy LocalSettings.php from old Wiki to new Wiki. Change the
database in the LocalSettings.php to the copy of your database.
Call home-of-new-wiki/mw-config (the adresse of the new Wiki) and follow the
instructions, this will upgrade the database to the new version.
If you are using a Windows server be aware that syntax highlight extension
will not work properly any more due to this problem
Sent from: http://mediawiki-i.429.n8.nabble.com/