바뀌다 is something changing on its own or being swapped for something else, and -(으)면 gives the trigger: '노력하면 바뀌는구나!' "so things do change if you try." A recurring shape here is 살다 보면 / 하다 보면 바뀌다 — as you go along, interests and people change of their own accord (인생을 살다 보면 바뀌는 것 같아요). Keep it apart from 바꾸다, which is you changing something deliberately; 바뀌다 is what happens to it.