If you need or want to remove CyberGhost open the Windows Control Panel, move to 'Program and Features' and mark the entry 'CyberGhost'. In the upper menu click on 'Uninstall', so the program and the also installed network adapter can be removed.
Removal of the CyberGhost client doesn't reflect in removing or deleting an existing subscription or a CyberGhost account. Both stay valid. Here you find how to cancel your subscription and here how to delete your account.