If you downloaded, did NOT save the original install file, and did not pay the $6.95 for "Extended Download", then you're going to need to buy again. This shows how to do so at Upgrade pricing, so you don't have to pay full price:
http://ftm.custhelp.com/app/answers/detail/a_id/5405/
http://ftm.custhelp.com/app/answers/detail/a_id/5405/