First, make sure that the files aren't "read only". If they are, right click the files, go into properties and Uncheck the box for read only. Hit ok and exit. Then to change genre, go through windows explorer, find the file, right click, properties, go into details and then click under Genre in the section marked (at the top) value. Type in your genre and then ok and exit. You can mass change file genres the same way by selecting any group of files.