Log in and navigate to your 'BSG Profile' at the top of the page in the blue bubble with your initials. Click on ' My Membership' in the sidebar and select your membership subscription from the list of active subscriptions.
Click to cancel the subscription.
Once this is triggered the page will refresh and you'll be notified of the cancellation on-screen. Return to the Membership page and repeat these steps for any other subscriptions (e.g. ESGE) if you are also a member of that society.