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From what I see on your account, the form FTP http://www.jotformpro.com/form/50436626968971 seems to be the one that have all the upload submissions.
You can view the form submission data and upload submissions in your My Form's View Submissions page.
If you need to lessen the current storage/uploads number of your account, you will need to delete the Upload field on the form to delete the uploaded files also.
OR delete submissions to delete also the entire submission data and the uploaded data.
Please take NOTE: Deleted submission data are permanently gone
So take extra caution before deleting them. Make sure you have a backup a copy of the submission data in case you need them for further use.
I noted that your jotform is integrated to FTP also.
If the submission upload data also already have a copy on your FTP account, it can be safe to remove the existing submission upload in your form. This will lessen your current storage spaced used on your JotForm account.
Hope this help. Let us know if you need further assistance.