Log in to the account you wish to delete. Click the "My Colleges" link on the left side of the window.
Click the "Remove This College" button under every college in the list. When you click this button, you will be prompted to confirm that you want to delete the college from your list.
Click the "Yes" button to remove the college. Repeat this process for every school in the list. This will ensure that you will not be contacted by any of the schools.
Allow the account you want to delete to sit unused until the end of the application season. The season lasts from autumn to the end of spring. Your Common Application Account will be deleted automatically during summer.