To edit your Monthbook Subscription book, first, be sure you are logged into your Chatbooks account and click "Bookshelf."

Click into the Monthbook you want to edit.

On the left-hand side you'll see all photos that are currently in your Monthbook. You can click on a photo and read the prompt to remove it:

If you tap "Remove photo," the photo will no longer be in the book and you'll notice it is no longer checked on the left-hand side where you can see all photos in the book.

Alternatively, you can scroll down once you're in a Monthbook, if you click on a specific photo, on the right-hand side, you'll see a "Delete" option under "Page Options."

If you want to add a photo back that you've removed, you can do so by clicking back onto the photo in the left-hand side where it shows all photos.

Learn how to exclude/remove photos from the Chatbooks here.