Yeah, unlike desktops... laptops do not really allow you to upgrade the graphics card / chip. Generally speaking only some of the $1,500+ gaming oriented laptops allows you to upgrade the graphics card and only specific models. There are a some $1,900+ which do not allow you to upgrade so you would need to check 1st before buying.
Anywaste, there are a few "lowly" laptops that allows you to unofficially upgrade the graphics chip, but the vast majority of the time it is simply soldered into place and the BIOS will not likely recognize a different model graphics chip.
"Discrete" for laptops means not integrated into the CPU or chipset.
"Discrete graphics" could be a graphics chip soldered into the motherboard which is the case most of the time, or a MXM format card at may or may not be soldered into a MXM slot (PCI-e 2.0 / 3.0). MXM cards are only used in very expensive gaming laptops and only specific models can be upgraded.