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.
Are you referring to this form - http://www.jotformpro.com/form/52101577250951? It seems that the Download All Uploads is only limited to 250 MB or 250 files.
You can try to partially download your form (download uploads by batch). You can try to filter it by date and download the form partially.
Basically the idea is similar with this article: How to Partially Download Form Submissions.
Do let us know if you need further assistance.