Short answer: through your account, at the shinywhitebox.com website.
- Login here: https://shinywhitebox.com/accounts/login/
- If you cannot remember you password; you can reset that by goingn to this link: https://shinywhitebox.com/accounts/password/reset/
- Go to the subscription tab:
- Click on Stripe Portal
- You will see the billing page from Stripe. Click on the 'Cancel Plan' button to cancel the subscription: