In order to delete the files, navigate to Settings > All > Apps/Applications, select the utility used to download the charts and tap Clear Data and Clear Cache. After that, download the charts again because this process should erase all the charts. Alternatively, open the File Explorer tool select Phone Storage, open the Download folder and delete the extra files. If you can't find them in the Downloads directory, look for the folder named as your application, open it and delete the files.
