Comment 2 for bug 1380224

> ERROR: The database format changed between beta 2 and 3. Please dump your 9.4 clusters first and remove them before upgrading the package.

Indeed. Sorry about that, 9.4 beta prematurely slipped into utopic. This is a safety measure so that you don't lose your existing databases after upgrading to beta 3. You need to make a dump of your existing clusters (using pg_dumpall), and then either remove the clusters using pg_dropcluster or purge the postgresql-9.4 package, and then install/upgrade the latest version.

Sorry for the inconvenience!