Hi julieo459,
The intention of the Unsold download request is to allow the user to Relist the items back to the eBay site as newly listed items. Its format is not designed to simply upload the file back. You will need to take the information, specifically the ItemID values, and create a new file.
For new users of File Exchange, we highly recommend that you review the Advanced Instructions PDF User Guide below:
http://pics.ebay.com/aw/pics/ca/pdf/file_exchange/File_Exchange_Advanced_Instructions.pdf
Page 14 explains how to Relist items to your account.
Downloading the Unsold items in FIle Exchange will not modify your Unsold folder in My eBay. The items will remain there unless you remove them directly from that section.
Regards,
Draex
eBay File Exchange Support