How can I delete the data for my account so I can continue to use the 100MB

We certainly don't need the storage space, in fact it seems rather undesirable to have you keeping data on our customers. If we receive a jotform response we download that info into our contact list. 

I have checked your account and you're over your upload limits.

You would have to delete the submissions with the upload files to free up some space.

Do note that once you delete the submissions, we cannot recover them at our end.

I would suggest downloading your submissions and uploaded files first before deleting them.

To download, kindly follow these guides:

https://www.jotform.com/help/73-How-to-Download-Form-Submissions-as-Excel-CSV-PDF

https://www.jotform.com/help/356-How-to-Download-the-Submission-Files

To delete:

https://www.jotform.com/help/377-How-to-Delete-Form-Submission-Data

Hope this information helps.