If you know what’s using that file (i.e.,an open instance of MS word will typically be using a Word doc), the easiest way to delete a file in use is to shut down the software and try again. Sometimes, the application will show an error, in which case you might want to force-quit the process. In Windows, you can easily do this from the Task Manager interface. If you don’t know what process is responsible, Windows Resource Monitor does the trick. Bring it up by looking for Resource Monitor in the Windows search box or by typing “resmon” in the Run command window. Go to the “CPU” tab of the Resource Monitor and type in the file/folder name in the box next to “Associated Handles.” That should tell you which process is to blame, and you’ll be able to kill it by right-clicking on it and selecting “End Process.”