Wont relinquish memory

When I attempt to upload a large video file, DS File soaks up the last 2.5 GB of iPhone memory preparing to upload, runs out of memory, and abandons the upload. But DS File holds on to the 2.5 GB! I can find no way to reclaim the 2.5GB other than to delete the app.

Sorely Disappoimted about DS file, v5.9.1