You need to enable the tool context to select Instanced Renderer with mouse. To do that press 'I' on keyboard or press context tool button. With that tool hold shift to select InstancedRenderers with mouse.

When that context is active, there is additional window in top letf corner of Scene View.

• Allow merged modification
  • enable to allow transform modification of all selected object at the same time.
    Disable to menage them individualy.