If you bought Pro less than 6 months ago, go here & enter the email address that you used to buy Pro.
http://sales.limewire.com/support/pro_lookup.php

If you bought Pro more than 6 months ago & didn't back up your Pro installer(s), you'll have to buy again. LW Pro entitles you to free updates for up to 6 months. It's the user's responsibility to save & back up their Pro installers