If you started working on a layout and realized it's not to your liking, you can easily either start whole book over - or just the current page. In the toolbar right above the book, click the "Clear" button. This opens a drop down with five options:
1) Clear All Images: This will remove all images on the current sheet but the layout remains.
2) Clear sheet: This will remove all images and the layout on the current sheet or page. Your sheet will be blank.
3) Clear Theme: This will remove the theme on the current sheet if one was selected.
4) Remove Sheet: This will delete the current sheet - but only if your photobook has more than the minimum required number of pages.
5) Restart: This will remove all images and layouts in the book. If this option is selected, your entire book, including layouts and image will reset so you can start over.