What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I'm not sure what you meant by you have clicked delete on the preview window. Are you referring on accidentally deleting the form? If you do, you can restore it by following this guide: http://www.jotform.com/help/134-How-to-Restore-Deleted-Forms
If you are referring to the actual changes on the form, if there's a previous version of your form that had those changes that were successfully saved before, you should be able to revert back to that state by following this guide: http://www.jotform.com/help/294-How-to-View-Form-Revision-History
Do let us know if that works.