How can I bring my son's blonde hair back?

my son has been coloring his naturally dark blonde/light brown hair with a cheap black hair color for about a year. He is finally sick and tired of the 'goth black' hair look, (yahoo!), but the color experts at Clairol told us he could not lighten colored hair and would need to go to a salon to have it lightened then colored. He wants me to do this at home but I am not sure how light to bring his bleached hair up to? And then, should I wait a certain amount of time (weeks?) before coloring the bleached hair? Needing all the help I can get to get back something close to my Son's beautiful dk blonde head.

I would go to the store... like wal-mart and get a little lighter color then his nature because of the black. but if it doesn't work then you'll probably have to go to the salon. sorry if it doesn't