To remove a learner from your account, make sure you are signed in to your guardian account.
For the learner you want to remove the account for click the three dots in the top right and choose Remove Learner.
You will then have the subscription details for this learner confirmed. Their account is live until your next billing date.
If you are happy you want to remove them, choose remove.
You can re-instate your learners account at any point.