It is really going to depend on what brand of hair color you have on your hair to begin with. To get a quick easy answer you should do a test strand. You will definately have to use bleach. To do a test strand mix a portion of the bleach in one to one form ie:one tsp powder + one tsp liquid developer. Take a small strand of your hair apply the bleach mixture and wrap the hair in alluminum foil to keep it from touching the rest of your hair. Then wait. If the foil becomes hot not warm remove the foil immediately and wash out the bleach. This only happens if there is a chemical reaction between the bleach and previous hair colors. Ocassionally this will happen with heat activated hair products. If there is no reaction that forces you to take the bleach out of your hair then leave the foil and bleach on the hair untill you get the desired color of blond you want. Be sure to start a timer the second the foil is put on the hair so you will know how long the test strand took to process. You now have an accurate time scale. If the bleach turns your hair orange you need a stronger developer. You can either mix the bleach with two parts liquid and one part powder or you can find a salon supplier that sells to the public and ask for 30 vol developer. If you get the developer go back to using a one to one ratio or you could melt your hair and or get chemical burns. Be sure to use gloves. If you are at all scared about doing this to your hair and can't afford a salon try your local beauty school. They will do your hair for a fraction of the price of a salon and there are professional hairdressers on hand to help.

Color remover first, then bleach. Then possibly a further lightener if your hair can take it. But color remover first.

Never highlight hair at home. You will end up in salon anyway., Just do it correctly. The tecnique and placement of foils or highlights is the key to the overall look. You cannot do this at home. Besides the fact that it will most likey be very brassy or very orangy.