If you can't delete an ISO file as the file is open in your System, check if it is mounted as a drive or not. Uses these proven fixes to resolve the issue.

To run it, search for Disk Cleanup in the Start menu, select the drive with update files (this is usually the C drive), and ...

One reliable open-source tool for securely overwriting and thereby deleting files on a Windows system is the aptly named Eraser. The program can be downloaded for free from various sites.