The correct option is
A It has changed a lot.
Option A: 'Has changed' is in present perfect tense. It states an action that has recently happened.
The person went back to their hometown after many years. Hence the change took place in that period of time.
'Has changed' describes an action that began in the past (many years back) and is still relevant in the present 'you went back'.
Hence option A is correct.
Option B: 'Had changed' is in past perfect tense. It states an action that completed in the past. But, the person 'you' sees the town and immediately reacts that it has changed, since the last time he was there. Hence the action is in present and not past.
Option C: 'Had been changed' is also in past perfect tense, in passive voice. It is irrelevant to the given situation.
Option D: 'It is changed' has a meaning different from 'it has changed'. The former clause means that 'it' is changed by someone, whereas the town has simply changed over time. 'Is changed' refers to a state of being changed, which is rather complex in meaning. 'Has changed' refers to the act of changing, which is much simpler to understand.
Hence options B, C and D are incorrect.