How to clear out the uploaded attachments

how do I clear out the attached items from my upload space (not the submitted forms)?  

To clear up your upload space you need to delete the associated submission, this guide will help you doing so: https://www.jotform.com/help/377-How-to-Delete-Form-Submission-Data 

You may also download your submissions data following 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 

I hope this helps.