When you bought pro, you will have received an email with a link to your own personal downld page. Simply go back to the email & find the link again. Otherwise go to LW's support page & press on Pro support. Unfortunately the page is down at the moment so you may need to wait a day or 2. http://www.limewire.com/english/content/support.shtml
But keep in mind, your pro free updates are only valid for 6 mths after you purchase it.