In case you determine that scheduled articles are not suitable or overlap with another topic, you can change the content or date of it. This requires that the article was not published yet.
Get to the campaign's left side bar "Your Facebook Postings" and to the tab "Scheduled Posts".
All scheduled posts are shown here. You can delete the complete article via the right buttons or reschedule with the underlying button:
If you cancel the article, a query appears in order to prevent accidential erasure.