When you are in the creation part of your book, click on the Global View button, at the bottom right of your screen.
You will then arrive at the overview of your book by double page.
To be able to move your pages, simply click on the double page you wish to move and then drag to the desired position and release.
To return to the creation part of the album, double-click on a page or click on the Page View button, at the bottom right of your screen.
Individual pages cannot be moved, only the double pages can be moved.