How do you get toned,shaped,cut,defined arms without bulking?

I goto the gym and I can't list too heavy cause my muscles strain but 6kg is light and just right. I hear light weight- high reps tones muscle but also heard it's a myth and that low reps high weight bulks it up and makes you have arms like the big show not like Hercules or the guys from 300(well defined) I also heard good diet and cardio but I want to know the truth of getting to show like defintion with deltoids sticking out with biceps no big straight biceps with no curves like sumos!! How do you get ripped and defined so that your abs show and arms are shaped I'm already lean or not fat.