For mac you can simply copy the program across. But make sure you keep the entire contents of the incomplete folder also (Open LW on your new comp & set up the preferences such as downld location, then close it. Then replace the incomplete folder with the one from the other computer.)
Otherwise you can re-downld it from the official site if you know the email & if it's still eligible for updates & downlds (within 6 months of purchase) HERE (click on link)