How do you make your hair color lighter?

I have naturally dirty blonde hair. I am a 14 year old male and my hair colour changes according to light. In the summer it is lighter according to the amount of sun and light. It can get so bright it can be a very light blonde. In the winter it is darker and sometimes can get so dark it seems brown! Currently I have the darker brown colour because it is the winter. What I am asking is how do I get my hair light blonde like in the summer?How do you make your hair color lighter?
Go to a salon and have then lighten in for you. Paul Mitchell's ';Lighten Up'; is fantastic, however only a hairdresser can use it on you.How do you make your hair color lighter?
If you do not plan on dying your hair or getting highlights u should go swimming often, like in an indoor pool. the chemicals make your hair turn lighter.