Take each individual letter and insert it into it’s own layer.  This is important because you can only tween one object in a layer in Flash, so each object that you want to animate has to be on its own layer.
The next thing to do is to double the number of active layers you have, by copying the ones you’ve just created and recreating them.  This is because each letter animation in fact involves two items: the letter you’re starting with, and same letter turned into a light.  Copy each of the layers you created containing a letter, and copy them into blank layers.  Remember to rename them, so you can distinguish between them.