^^^Good advise for an experienced grower, not so good for a newbie. Best to learn how to grow before you learn how to optimize your grow to suit your needs. Too easy to go overboard and stress 'em further than is necessary.

Were I you, I'd try and find-out why the lower growth died, and concentrate on not letting that happen any more. Was it because the light wasn't strong enough to penetrate deep enough? Or from plucking too many fan leaves? Or too many additives or nutrients? A bug problem?

Till then...supplimental side lighting (CFL's?) is a good option to help this plant fill-in, but results are not guranteed.