Our editor makes it very very easy to add pages to your project. In your project middle bar (just above your album itself, where all the editing stuff is) you can add or delete pages. Here is how it looks:
You can see at the right side insert page and delete page.
Insert page will add 2 pages (left side and right side, you cannot add just one) at the end of your project.
Hitting the delete page will delete the 2 sided page you have selected. You will be shown a prompt to make sure you really do want to delete the page. This is how toe prompt looks
If you hit the green V than your page will be deleted.