Unless you have a lot of hair color knowledge, when lightening that much you might want to have it done at a salon by a pro. Many over the counter box dyes (permanent color) don't have the proper level of peroxide to effectively lighten you. That box has no idea what your natural level is. Many people turn an ugly shade of orange when the pretty girl on the box has a beautiful caramel blonde. Also, if you already have color treated hair, color will not lighten your previously colored hair. So your results can be very uneven and disappointing
However, if you want to do it yourself, you could opt for a demi permanent color to change the tone of your hair. It doesn't travel as far into the cuticle and the level of peroxide is VERY low. So there's less damage and you get more predictable results..