Is there a high speed train from Guangzhou to Shanghai,do we need to transfer train halfway?

There is no high speed train from GZ to Shanghai. If you want to take a high speed train, you need to transfer in Changsha or Wuhan.
The high speed train from GA to Wuhan takes around four hours and a half and from Wuhan to Shanghai, it takes around 6 hours.

The trains from GZ to Changsha takes almost around three hours. The bullet trains from Changsha to Shanghai takes around 7 to 9 hours.