How do I remove a form theme?

I added a theme to my form and I don't want it any more. How do I return it all back to default? 

Thank you for contacting us.

Please use a revision history tool in order to restore your form to the previous version.

How to View Form Revision History

I have also attached a ticket to this thread to see if we can add a plain remove theme option. It will be considered by our Development Team.

Let us know if you need any further assistance. We will be happy to help.