For these steps to work you have to be the purchaser of the membership(s). If you are not the billing user, please contact the person who shared the membership with you.
If it is a membership that you shared with someone else you will see the "Release" option listed at the bottom of their card. If it is your own membership you will see "Forget Membership" listed
Choose either "Release" or "Forget Membership" respectively, and confirm your action on the subsequent pop-up message.