A scheduled Booktrovert campaign cannot be edited. Instead, first cancel the campaign from the confirmation/receipt page. Once you do this, a new draft version of the campaign will be created, which you can then revise and reschedule. (Note: You will also see the original version of the campaign in "History" with a "Cancelled" status.)
To cancel a campaign, click Campaigns in the top navigation, and then “Current + Scheduled”. Next, click the campaign name to open the confirmation/receipt page, then click the "Cancel Campaign" link toward the top of the right-hand column.