If you have already downloaded the new TomTom GO mobile app, you can uninstall the TomTom Navigation app. The steps to uninstall an app can be found on the FAQ page on Google Play.
Please note that the map that was downloaded for the TomTom Navigation app may still remain on your device. This will be automatically removed when you start the new TomTom GO Mobile app, giving you space to download the latest map for your new app.
For other ways of making more space on your device, visit the FAQ page on Google Play.