If you want to delete the voice guidance files, you will need to uninstall and reinstall HERE Drive:
- In the apps menu, tap and hold HERE Drive and select uninstall.
- Start Store.
- Reinstall HERE Drive from Nokia Collection or search for "HERE Drive".
Note that you can have several voice guidance files downloaded on your phone and you don't need to delete them to start using another voice guidance. Simply select the desired voice guidance in Settings > Navigation voice. The size of the voice guidance file is relatively small (the size can be seen in the Download new menu). Having several voice guidance files on your phone shouldn't cause any issues with your phone's memory.