How can I become immortal?

Taoism believes that people who eat grains will produce dirty gas in their bodies, hinder the road to longevity, and can break grains. They are the root of desire, and they live by food and gas. If they don't eat whole grains, they will get rid of these three kinds of worms. Without all kinds of desires, mortals will be more aware. Taoism aims at cultivating immortals, which is also a process from ordinary people to immortals. But no one in life can cultivate immortality.