Googled some ideas - they all seem pretty easy to do:

http://www.ehow.com/how_4898186_unsh...l-sweater.html

http://wiki.answers.com/Q/How_do_you_unshrink_wool

http://bryanong.blogspot.com/2007/07...-sweather.html

http://consumerist.com/consumer/tips...ool-267551.php

http://www.thebudgetfashionista.com/...wool_sweater2/