When a new version is being released, it is usually not immediately available via upgrade (especially not as upgrade from the old version). You will have to download the whole new installer package.
The client seems not able to tell apart a "minor update with new network version" from a "major upgrade to a whole new version", it always displays the suggestion with the updater - no matter it if really is the recommended solution.
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I read in the german community that it may be possible to update from 0.5 RC2 about during the same time as the installers for the (not really...) final release become public.