How to remove a theme and reset the form to the default theme?

I created a new theme on one of my forms named 'Playa Vista Soccer Academy' However there are problems with the new theme. I cannot change the field entry font color and because the background is white customers cannot read their white font as they type. To counter this I made the field background color a deep Blue. But this is not the solution I wanted. It now looks confusing and not user friendly. So I want to reset the form back to the original default theme. However the system will not allow this either. Please can you help with this issue.

Thanks

You may delete all the form that you have injected.

You may also consider reverting your form back to a previous version, please take a look on this link: http://www.jotform.com/blog/95-Introducing-Form-Revisions-Never-Lose-Your-Work-Again-. 

You will be able to find the change in your form history and revert it back to that version where you did not apply the theme.

Hope this helps.