Portrait Mode in Keynote
Last year someone asked how to change a slide in Keynote from landscape to portrait. The answer does not look like anything I see in Keynote 10.0. I don't know what Inspector is. There is no Document pull-down menu. The Slide menu does not have a Size option or a Custom Slide size.
Neither the Format nor Document icons bring be to a screen with a Portrait/Landscape option. The Search box under the Help menu discusses how to do this in Pages. Nothing about Keynote. There is nothing in Keynote's User Guide for Mac.
How can I change a slide from Landscape to Portrait?