I bought a Theme but can't install

How can I upload Cornerstone theme unzipped?
When I download it I only get a contents folder instead there seems to be a screenshot.png missing from the zip file in the folder. which I assume is not what WordPress.org Codex site requests.

You can check the theme documentation for how to upload the theme.
If you need some -paid- help, I could offer one of my services :

As was intended, I was only suppose to use the cornerstone plugin but I should have downloaded X-Theme written by Michael Beckwith. So thanks for your input, though.