<p>I don't think it's a big deal but for the sake of accuracy I would send them all a brief letter explaining you made an error. They will appreciate your honesty.</p>
<p>I guess I would send a letter because it is more likely to get put into your file. If you have access to a fax, that is one way to make it quicker.</p>
<p>Don't send them anything. Admissions offices are already busy trying to put everything together and something minor like this will only take time away from it.</p>