How can I change my black hair into brown?

Going lighter is usually best done by professionals.

You can do highlights so your hair appears lighter, or do an all over permanent hair color that will lighten your hair. Hair can turn red, or not come out at all what you hoped for when going from very very dark to lighter, so if you try to do it yourself, just be prepared that you might have to pay to get it fixed. It might work out fine doing it yourself, which would be great.

You can call Miss Clarol help line if you’re in America and ask for advice, which product in their line they recommend.

I agree go to a salon as she may place a blond lightener on it and done professionally it wont’ be brassy and require solutions again to fix.
I dyed my grayish hair light brown and was using that particular shade for weeks but soon my local store no longer carried it! As my roots were unbecoming I almost dyed it a dark red as in the far past that she looked good on me and added a boost of colour to my complexion ( olive).
I tried a test on a quarter inch stands of hair and highlighted it….it was way too light and ruined the test strands making them stringy and unmanageable.That was it..I finally telephone an old hairdresser of which I stopped going to who fixed the problem for me for a whopping $135 plus $10 dollar tip as it took a grueling 3 hours to fix it.
I opted to go back to my natural colour with silver highlights of which I will return in a few months to add more so that I will not have to ever dye my hair again as with the silver tone my own grey will blend in naturally. Save yourself the trouble and get a Professional to consult..perhaps dark red is better for black hair rather than lightening it…as it gets costly every 6 weeks!

You could use CRISPR technology to alter your DNA to insert a brown hair gene in place of the black hair gene. Or you could just dye it.