In Composer, select the More Actions button, either on the bottom toolbar of the page you wish to delete or next to the page in the list.
Select "Delete" or click on the trashcan icon at the bottom of the Composer window.
Confirm that you are ready to delete the page and any sub-pages that fall under it.
Note: Unlike in Page Manager, you do not need to publish the page again before the deletion is final. This step cannot be undone.