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.
Upon checking your account, it seems that you have finally found the form or forms that filling up your upload storage space.
To answer your question, yes that is correct, for Free or Starter plan you can delete the submissions that has uploaded files on it to free up your space. I would recommend that you check our app integration regarding File storage and sharing services here: http://apps.jotform.com/category/file_sharing_and_storage. You'll be able to directly upload your submissions and the file uploaded on it directly to other storage services like "Dropbox".
You can also transfer using FTP, you can follow this guide: http://www.jotform.com/help/177-How-to-Enable-FTP-on-Form-Submissions.
You may also check this guide regarding file upload size limits: http://www.jotform.com/help/33-Changing-the-Upload-Size-Limit.
I hope this helps.