You can delete page(s) and/or spreads of a publication.
Click on the 'Overview Pages' button in the top left corner of the publication.

Now the overview of page(s) and spreads shows of the publication.
Click on the 'Trash' button of the page(s) or spread you want to delete.

Now there will appear a warning if you want to confirm deleting the publication item and all of its data. Click on 'Delete' to confirm.