Can I convert a landscape-format book to a square format once I've created it?
Square books cannot be converted to landscape format, and landscape books cannot be converted to square. If you created your book in a square format, you can order it in any available square size for that style (for example, 8×8 or 12×12), but it cannot be changed to sizes like 11×9, 8×6, or 14×11.
If you’d like your book in a different format, you’ll need to start a new project in that format.