Merge layers?

I have two layers in my movie, one with the walkcycle of the feets and one with the arms. I made them in two layers cus it was easier to edit them and fix them. but now i want the arms layer to be in the one with the feet. How is that posible in a fast way? I know i can copy / paste every frame in my walk. but thats way hard , and takes long time! Anyone got a good anwer for this?