Depends on the model, but generally the MX series and other lower end GPUs are soldered to the motherboard. Only very high end GPUs generally get treated to the add-on card experience. Even then they are rarely upgradable outside a generation or two, if at all.
Ultrabooks and other slim designs also generally have the GPU soldered to the board.
Most of the time upgrading a laptop GPU is not possible. That's one reason why I kind of dislike gaming laptops. But hey.... It would be hard to cool a much more power hungry GPU on the same old cooling system.