Isn't it the case the generally speaking, majority if not all GPU's are soldered to the Mobo itself? So in upgrading you'd need to remove where the previous GPU was, clean it up, then just check the Mobo manufacturers spec as to whether the upgrade will be compat? If all is green for go, re-attach the GPU to the Mobo and jobs a goodun (after drivers are installed obviously).
Some laptops use a standard interface where the graphics card is on a seperate board which slots in, so you can swap these boards like swapping the cpu.