Hi,
The download area is here:
http://simplylightwave.com/lightwave-tutorials/
If you click on the individual download links for parts at the bottom of the tutorial pages it will tell you if you've downloaded the video before or not, and you'll be able to redownload any tutorials from the past.
In case you don't remember which tutorials you purchased since it was a while ago you can e-mail
admin@simplylightwave.com with the account user name(s) or e-mail address the account is registered to and we can look it up in the database and send you a list.