On a new software release, provide first-time users with brief modules of content to show them the most noteworthy new additions and changes. These modules would number roughly 4-8 and appear only once per user. When first displayed, user would have the option to dismiss all or view them. On second login with the new release, they would not appear, but could potentially be retrievable via the help menu.
An example is when a user opens a workflow they built in the old workflow builder in the new workflow builder for the first time, the connections may be poorly drawn and labels overlapping. A tutorial popup could explain how to correct this, introducing how to use the new workflow builder.