Hi PalmTreeMary19,
weklcome to the Apple (user-to-user) Community!
Re: "Changing default margins for a Pages Booklet: My problem is that the TOP and BOTTOM MARGINS
are too big and I'd like to reduce them so I can make the printed body area larger."
See Apple Support's online article for a word-processing document:
Set document margins in Pages on Mac - Apple Support
Eg: says:
If you’re working in a word processing document, you can set the top, bottom, left and right document margins.
In a page layout document, you set margins for headers and footers.
Your settings apply to the whole document.
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Re: "I have changed the margin settings to zero; I have unchecked 'constrain proportions'"
In a page layout document: There may be space allocated at top and bottom for headers and footers:
You may need to delete headers and footers if any are set:
Eg: Apple Support's article: Add and remove headers and footers in Pages on Mac - Apple Support
says:
"Turning headers or footers off, removes the content from all headers and footers in your document.
- In the Document sidebar, click the Document tab.
- Deselect the Header or Footer tick box.
Note: If you change your mind, press Command-Z on your keyboard to add the deleted text back.
Simply selecting the tick box again won’t retrieve the deleted text."
All the best :-)