Once you've built your survey it's good to test it works how you thought. But you might not want those stats and test responses going forward.
To delete these all you have to do is delete a row in the Response List.
In the table that lists all of your Surveys, click on the three dots at the right end of the row and click Response View.
Scroll to the right end of the row you want to delete and click on the trash can to delete it.
Beware: Once you delete a response it is deleted from our database and cannot be retrieved. It is not backed up.