Change of Flight Itinerary Before Arrive in China

I bought a flight to Shanghai and gave that flight itinerary to the Chinese Consulate when I bought my Chinese tourist visa. Now I may need to change my arrival and departure dates by 1-2 days each. Do I need to give the new flight itinerary to the visa office, or to someone in China? Or can I just use the visa to come to China on the new itinerary without notifying anyone on advance?