Religion can be changed in India but a caste can certainly not be changed. A person born in upper-class caste cannot avail the benefits reserved for SC/ ST or OBC and vice versa. One acquires caste by birth. Yes, if there is an error due to many circumstances, you can certainly get it corrected by not entirely changed. All in all, caste is still not autonomous and it is not a person’s own decision. It can be changed in special circumstances, if your parents belong to different castes, you have a choice to one of their castes.
Caste change can be achieved legally only when someone has been adopted. And if a child born in an inter-caste marriage when attains the age of 21 chooses to vote for another caste of the father or mother in specific circumstances. In case of marriage, it is not legally possible to change from Scheduled Caste (SC) to Other Backward Classes (OBC) or religion, as instructed by Supreme Court.
In a judgement, the apex court of India ruled that the caste is decided as per the kin of birth. It can not be changed through marriage. If a woman of a general caste, no matter what the ritual says, she cannot change her caste legally and avail the benefits available to SC. Similarly, men also cannot change their caste through marriage.
Reference: Article 15(5) of The Constitution of India