Some tips on how to dye my hair...?

I have black hair (Japanese if that helps), and I just bought this dye Hoyu Bigen Silk Touch Mystic Violet. Before I got the dye, I asked the lady if I had to make my hair lighter to get the color on the box or if I could apply it directly on because it says that the dye is for Asian hair. And she said that I didn't have to lighten it, I would have been reassured but sadly I don't think the lady really understood me...So if there is anyone that knows about this kind of dye, do you think I should just directly put it on my hair without lightening it? Or should I just lighten it just in case? Thanks!!