Explain how, according to Hinduism, someone can be re-born into a higher caste

The basis of all Hindu morality lies in the idea that each caste has its own duty (dharma). When the body dies, the soul faces its destiny (karma) transmigrating to a lower or higher body. The Hindus believe that those who faithfully follow the path of duty (dharma) in the next reincarnation will be reborn in the next higher caste. The person who violates his dharmic duty will be reborn in the belly of an outcast mother or even be born in some animal species.