If you want to turn off CyberGhost and continue using your internet as usual, all you need to do is disconnect. To do so, open the app and click the disconnect button. Following that, you can also opt to exit the VPN if you want to.
If the app has frozen (potentially also cutting your internet because of the automatic kill-switch), you can opt to exit the VPN from your task manager. Following that, restart the VPN and disable the kill-switch to regain access to your internet without the VPN.