Editing a campaign that is already running
A running campaign is changed rather than stopped and started again. Open Campaigns, find it, and choose Change this campaign from its menu.
The two fields that move money:
How many you ordered. Raising it charges the difference; lowering it gives part of it back.
Watch length, on views, because a view is priced by time.
Both settle at today's price rather than the price the campaign started at.
Everything else is the shape of the delivery — priority, country targeting, how fast it goes out, how long before the same viewer counts again, and the words on a comment campaign.
One floor you cannot go under: what is already delivered, plus what members are working on right now. That work is done and paid for, and the panel names the number.
Only a running campaign can be changed. A finished or refunded one cannot — start a new one.