Why is upload space full and forms are empty?

The upload space will include all the uploaded files in all of your forms. I can see all five forms with file attachments.

Here's how to delete your submissions https://www.jotform.com/help/377-How-to-Delete-Form-Submission-Data.

Here's a link https://www.jotform.com/help/408-Understanding-Your-Account-Usage-and-Limits for reference on how usage limit works.

Let us know if you have any questions or if you need further assistance.