The method for going blonde depends on the original color and target level of lightness. For anything greater than three shades of lightening, hair bleach is required. Lightening more than five levels or trying to achieve platinum blonde necessitates visiting a professional hair stylist.
First determine the difference between the natural shade and target color. Use the hair swatches at a beauty supply store, matching them to the hair at the roots. If the difference is three or fewer levels, choose the desired blonde shade and a suitable peroxide developer: 20 volume for one level, 30 volume for two levels or 40 volume for three levels. Working in small sections, apply the color 1/2 inch from the scalp to 1 inch from the ends, pulling it through for the final 10 minutes of processing.
If bleach is needed, use the same application process. Mix the bleach according to the manufacturer's instructions, and apply. Cover with a plastic cap. If possible, apply external heat. Hair lightens to the target level of lightness and is likely to have brassy tones. Brassiness cannot be removed with bleach; it must be toned. Once hair is light enough, shampoo out the bleach, and apply the toner. Typically the toner is on the opposite side of the color wheel to the brassiness and is therefore either purple-based or blue-based. Leave the toner in until the target shade is achieved.