The best way to delete your old tours is to use Panoskin's Import Tool. When you import your old tour into Panoskin, it will download all of your scenes into Panoskin. From there, you are able to unpublish the tour from Google.
An alternative to deleting your old tours is through your Contributions on maps.google.com. As long as you are the owner of the photos on Maps, you can request to remove them.
This Google Support article walks you through how to delete photos using Google Maps: Add, remove or share photos in Google Maps