All you need to do is navigate to the page you'd like to remove, and click the edit tab.

 

 

Then, scroll to the bottom and click the "delete" button.

 

 

If you're deleting a book with child pages inside of it, it will warn you, and let you know that they'll be automatically reassigned to another book, and confirm that you wish to perform this action.

 

 

 

 

If you're deleting a book page , it will ask you to confirm it as well.

 

 

 

Click delete, and a confirmation message will appear. Or, you can click "cancel" to cancel the action.