How do I ACTUALLY delete a file

I am using Delightful Downloads version 1.6.6, on WordPress 4.7.3 hosted on Amazon Web Services Lightsail (which I think is a UNIX machine).

Would someone please tell me how to delete a file from the Delightful Downloads directory? When I replace a file in the “Downloads” tab, I see that my new file doesn’t actually replace the old file. Instead, Delightful Downloads keeps the old file and gives my new file a new name (with a suffix of “-X”, where X is the number of replacement files). I can’t seem to access the directory from the WordPress administration portal. When I do an SFTP into the directory, I can’t delete the files because I don’t have the proper permissions.

Finally, and most frustratingly, when I delete a file in the “Download” tab, even when I permanently delete it from the trash … the file itself stays in the Delightful Downloads directory. I also don’t have access to it from the “Media” tab in the WP portal.

Thanks,

Nate