If you used a one-off Premium or Milestone board, there is no need to cancel it because you are not on a subscription as it was a one-time purchase.
If you want to cancel a subscription (to a Starter, Business, or Enterprise plan) - you can do so directly from your account page. You will retain access to all the features and benefits of your plan until your lapsed renewal date. If you run into any issues, reach out to us at help@kudoboard.com and we can assist.