Apple downgraded my out of warranty series 0 aluminum watch for free to watchOS 3. What they did was send me a replacement watch running watchOS 3. The pleasant surprise was that it is a series 1 watch. So happy to be back on watchOS 3 and very very happy to have the much snappier series 1.
I need to do this as well. Do you know if in store can downgrade/replace or must it be shipped? My series 0 is out of warranty and just don’t want to be denied.