color

Is your hair permanently coloured dark brown? If it is, you can't lighten without using a colour remover first. That may be best left to a professional because it might not remove all the colour on the first try; you may need to bleach too. It could turn disastrous. You could really damage your hair.

If the dark brown you mentioned is your natural colour (with no dye in your hair), you could use a single process permanent colour to lighten your hair about 2 shades. If you want to avoid reds, use an ash tone. Before you put anything on your hair, though, make sure you do a test strand first.

Good luck.