I think those instructions were written when the Betas were first made available. Recently, up until RC12 or 13 it has been perfectly feasible to upgrade the Beta using the option within the app. Sadly, some sort of change in an update to Qt at that point has been causing the internal updater to fail and crash Scrivener. So for the moment you have to do a manual install until the devs can work round it. You can read about it in this long thread:
