Please tell me how can i get taller?

Hi every body, I am Ras and i am male and i am almost 20 years old, my height is about 170cm (5.6 feet) and i want to gain 2 to 4 more inches, and i know for some reasons it is not very easy, but there is alwayse a hope for everthing, so is there any body who would like to help me with that (know any website, or any methodologies that can help), i will storngly appreciate that.