Open your Lemon Squeezy orders, sign in with the email you bought with, select the Ghost Kit Pro subscription and cancel it. The receipt email links to the same page.
The license stays valid until the end of the paid year, and nothing is charged after that. The plugin keeps working after the license expires; what stops is updates and support. See What happens when my license expires?
If your receipt came from Paddle or nkdev.info, the subscription is managed in the nkdev.info account instead. See Licenses bought through Paddle.