I would like to go to changzhou, which I think I got to arrive at Shanghai from Singapore.

There is no direct bus or train from the airport to Changzhou, you can take the following route.
If taking a bullet G train, I suggest you take the shuttle bus line 1 to Hongqiao railway station. The train’s travel time is about 70min, and the fare is CNY74.5 for the second class seat, CNY119.5 for the first class seat and CNY239.5 for the business seat.

If taking bus, you can take the shuttle bus line 7 to South Railway Station, and then walk to nearby South Long-distance bus station. There you can take the bus to Changzhou. The bus is scheduled at 07:33, 09:31, 10:43, 13:11, 13:59, 15:43 and 18:41. The bus fare is CNY68 – 70, and the journey time is about 2.5 hours.