Most shampoos claim to "brighten" already light-colored hair, but I've never heard of one that actually lightens the color. I've used products like Sun-In in the past to lighten my hair--you use it like hairspray after you wash your hair.
Lemon juice, chamomile, baking soda, and sun exposure are great natural ways to lighten your hair color. Also, John Freida makes hair-color specific shampoos that work great!
There are shampoos on the market that will alter your hair color, but it's a lot harder to go lighter instead of darker without use of chemical products. You could use products like sun in that will lighten it along with sun exposure. The best way to lighten hair, is to get it dyed.
There are many shampoos that will lighten hair color. One that works particularly well is called "Shimmering lights." It is in a purple bottle and you can buy it at Sally Beauty Supply for eight dollars. There are also a lot of home remedies that are said to lighten hair. You might want to google some and check them out.
If u find one, its probably horrible for you. A shampoo shouldnt lighten your hair. If you want to lighten it u can go to the store and get hair dye or u can get in done professionally in a salon.
Most shampoos available for blond hair simply leave a reflective coating on each strand of hair, which can actually make hair appear darker. Many formulations prevent this but for actual lightning try going into the Hispanic section of hair care and look for chamomile fortified shampoos.