In order to delete one of your existing ad campaigns, log in and navigate to your AppyAds membership page. Find the ad campaign you wish to delete and click on it as if you were going to modify the campaign. You will be taken to the Edit Campaign screen, where you will see a Delete (trash can) button in the upper right corner of the General tab.
Simply click on the Delete button to have it removed. You will be shown a small dialog asking for you to confirm that you really want to delete the ad campaign.