The task to upgrade Alfresco (Community or Enterprise) from a version to another more recent, has to follow a clear and precise path. In every case it is always a critical task and in some cases could be a serious problem for the Organizations (of course this is more critical for Community Editions). In some cases the only possible solution is an Alfresco-to-Alfresco migration instead of an upgrade… but this is another scenario.
In this tutorial is described a step-by-step approach to an upgrade from an Alfresco Community Edition v4.0.d to v4.2.f in one only upgrade step. In every case, even if the involved versions are different, the approach is always the same discussed here.