<p>How do you let the other colleges know that you don't plan on attending? Write a letter? What would it say?</p>
<p>Dear College X,</p>
<p>Thank you for extending the offer of admission but I have decided to enroll elsewhere.</p>
<p>Sincerely,
applicant</p>
<p>You should get a letter from each college you're accepted to (and waitlisted at that) to either accept or thankfully deny the offering, which you mail back.</p>