There are three different types of graphics cards or graphics chips in Notebooks:
- External graphics cards which can be plugged into the notebook.
- Internal, dedicated graphics cards, e.g. Chip soldered on the Mainboard
- Internal, integrated graphics, which are a part of the CPU.
With the first type, an exchange of the GPU is usually not a problem, some manufacturers have their own type of proprietary connectors for external GPUs you can purchase and connect one from them directly. There is also Thunderbolt 3 which is present on some modern Notebooks. It allows the connection of an external graphics card from any vendor.
If your GPU is soldered on the mainboard either as a dedicated GPU chip or as part of the CPU an upgrade is almost impossible since it would have to be soldered on and also usually only one chip is compatible with the motherboard and firmware.
Even if the GPU is in a slot like the MXM-slot, which is often found in older laptops, an upgrade is usually not possible. This is due to some measurements not being standardized, the cooling solution not being able to handle a more powerful card or firmware issues.