Nope, as with pretty much all laptops there's no scope for a GPU upgrade. AFAIK the Defiance has a soldered GPU but even if it had a removable GPU you wouldn't be able to upgrade to a Pascal GPU due to it having different connectors to previous gens.
I think the GPU is soldered into the motherboard but even if it is possible upgrading the GPU is not cost effective and in some cases not possible if clevo does not release a BIOS update