My hair is black and i want to dye it ash blonde with brown highlights what do i do??help?

i know that i have to bleach my hair but is that by using blue powder bleach with 40% and do i apply it all over including my scalp?or is bleach not meant to touch your scalp?i know thi will make my hair an orangey colour but just worried about bleaching my skin/scalp.thanks for any answers