User blog comment:Ohmyn0/Making your wiki HTML5 compliant/@comment-25125639-20120705181353/@comment-118323-20120705200756

If you're speaking about upgrading to MediaWiki 1.19, we'll do that for you automatically. We have hundreds of thousands of wikis to upgrade so we're doing them over time, not all at once.

Updating your wikitext is another matter -- you can either do it by hand or you could use a bot. Try asking on the Forum for helps with bots!