There is actually not an easy way to delete the old ads or ad sets you create, but there is an important reason for it.
Old ads and ad sets collect data, and if you delete them from your dashboard you lose the ability to view that data and gain insight into your past campaigns.
The data from past campaigns provides you with valuable insight you can use to guide your current and future strategies.
Instead of allowing users to delete campaigns, the Brainity puts ACTIVE ads/ad sets automatically at the top of the list so they are easy to find.
Additionally, you can edit the name of the ad that you no longer want to use, to make it clear to you or anyone on your team that you don't want to use it anymore. For instance, you can change the name to the date you were using it, or write "OLD" in front of the name.