You can delete a user who should no longer have access to your account. However, this can only be done by the Account Owner.
You can do this action through Account Settings > Team Details.
To do this, click on the ellipsis for the user (Pending or Activated), and choose "Delete" from the drop-down list.
You will then be asked to verify your request by typing DELETE to confirm.
Once completed, that user account will be removed from your account.