The first step is to stop chemically treating your hair weeks before using peroxide, as this process requires hair to be healthy and damage free, you need to stop colouring your hair as well.
You first need to hold a test before you proceed to treat all your hair with peroxide. Just cut a small lock of hair from an area which can be covered by other hair.
Now you can tie a thread around it to do a strand test. This test will give you a preview of what colour you will get after treating the hair with peroxide.
In this step you have to mix a solution of hydrogen peroxide with water and then pour this solution in a spray bottle. Thoroughly spray this on your hair and then comb it afterwards. It is recommended that you leave it on your hair for about 15 to 20 minutes before rinsing.
You now need to highlight your hair by choosing to colour the desired strands. It is always better to treat hair in strands instead as a whole. Apply peroxide to these strands when they are wet and leave them be for 15 minutes before rinsing.
You may have to apply peroxide more than once if the hair are not lightened according to your desire.
Once you have achieved the desired results, you then need to use a conditioner on your hair as peroxide dries your hair which can lead to breakage. With deep-conditioning however, you can protect your hair.
If you think this is too difficult for you to handle and you might mess up your hair badly, then you should seek help from a professional hair stylist.