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.
The screenshot below depicts Windows 10.
Removal of the CyberGhost client doesn't reflect in removing or deleting an existing subscription or a CyberGhost account. Both stay valid.
Here you will find how to cancel your subscription and here how to delete your account.
For receiving a refund, a request will need to be submitted as cancelling the subscription or deleting the account will not trigger a refund. Only Support can help with receiving a refund. Make sure to check the Money Back Guarantee policy as well.