I can't work out to do this.
If I remove the old window by marking it "Demolish" in the renovation palette, the opening is shown blocked up, and a new opening formed for the new window, which of course is incorrect.
How do I remove the old window and provide a new window to the same opening?
Change the status of the existing window to To Be Demolished, as you have done. Then place another window that has a Reno status as New at the same place as the demo window. Then check that you have the correct Renovation Filter selected for your View to see the old window as demolished or the new window in place.
Check that the Renovation Filter Options for that View are set to:
Existing Elements: Show
Elements to be Demolished: Override (so the line types are changed to dashed)
New Elements: Hide
That should show the Existing as is, the Demo as dashed, and hide any New elements.
The Renovation Filter setting is assigned to each View, similar to a Layer Combination.