If you have an old smart campaign that you don't need anymore, you can delete it. Here's how.

Be sure before you delete. Once you delete a smart campaign it cannot be restored.

Go to the Marketing Activities area. 
Navigate to your inactive smart campaign. Under Campaign Actions, click Delete.

To cancel processing of an active smart campaign without deleting it altogether, learn how to abort a smart campaign.

Click Delete to confirm.

Do NOT delete an active smart campaign with people in the flow steps. The campaign will likely still execute.

Nice!