In Kafka's novel entitled Metamorphosis, a man wakes up to find he has turned into a cockroach. That kind of complete and startling change pretty much sums up the word.
When a caterpillar becomes a butterfly, it goes through a metamorphosis. An idea can undergo metamorphosis, or metamorphosize, too as can feelings. After you spend a full summer with your grandmother, your feelings about the woman may undergo a complete metamorphosis. While you were once afraid of the old woman, you now love her dearly.