Global text editing?

How do I change the font in an entire document, with subdocuments?

I’ve I select the top document (which is Manuscript). I select the font I want. But when I move the cursor throughout the document, I can see it was not changed globally.

You can’t select across scrivenings sessions, if that’s what you’re trying to do. But if you’ve changed the settings in Tools->Options->Editor, you can apply them to multiple documents by selecting them all in the binder and going to Documents->Convert->Formatting to Default text style.