Our next schema change version will be released on Monday, 18 May, 2015 around 10am PDT/1pm EDT/17:00 UTC/18:00 BST/19:00 CEST. We expect that MusicBrainz will be unavailable for 15 – 30 minutes during this time. We will put up the downtime notification on the site and tweet from @musicbrainz right before the release.
Since we’re total slackers, we still haven’t set up our backup database server since it suffered a hardware failure. This means that we won’t be able to put the site into read-only mode and will require us to do a full downtime. Hopefully for our next schema change we’ll have tackled our backlog of sysadmin duties and will have a backup DB server to make the release easier.
Sorry for any trouble this may cause you.
P.S. Look for another blog post on Sunday for details on where to get your access tokens for the Live Data Feed.
MetaBrainz Blog 
I have a musicbrainz vm server. How do i go about doing the upgrade ?