Ms,sandy, you could take bullet train from Beijing to Shanghai, which takes around 10 hours. Take the following information for your reference.
Train D321 (Departure Time 21:15; Arrival Time 07:22)
Train D313 (Departure Time 21:20; Arrival Time 07:32)
Train D305 (Departure Time 21:40; Arrival Time 07:52)

Besides, you could also take train T103 or T109, which take around 13 hours. These two trains depart at 22:00 and arrive in Shanghai at around 11:00. Check the detailed information in this webpage: https://www.travelchinaguide.com/china-trains/

If you take flight, it will be 2 hours. But the airfare is higher than train. The following link has the detailed information you need: https://www.travelchinaguide.com/china-flights/

Hope it helps.

Bullet train: 10 hours from Beijing to Shanghai. Train is better. They are night trains and will save a day on the way. if you want stop for a while in SHanghai, suggest you go by train.