From book editor, click "all pages" to see the order of all the pages in your book. To move an image, simply click on the image and hold down to drag and drop it into place.
If you want to move several pictures to a different part of the book at once, select the images you want to move by clicking the circle in the left corner of the images, then either drag and drop or use the "move to" selector at the top of the screen to move the images to the desired part of the book.
