To change the ads: switch out the ad code in the “Value” for the Custom Field that refers to which ad you are changing (for example, if you want to change the top index page ad, then switch out the “Value” for the one with “Name” attribute of “ad-index-top”)
For the category pages, the “Name” for the ad is “ad-category-slug”. So for the “Travel” page, find the custom field with the “Name” attribute of “ad-travel”.