To move up it after each life (reincarnation) by gaining good Karma-- when you reach the top and have good karma, you go to live with the universal spirit. Top of caste system: Priests Bottom of caste system: untouchables
Karma is all the good or bad things you do in life. If at the end of life you have “good karma,” you’ll move up the caste system when reincarnated. If have “bad Karma” you’ll be reincarnated down the caste system, or possibly be reincarnated as an animal.