Impossible !
Your laptop's graphics "chip" has either no memory at all or its own small memory reserve and when it is not enough "takes" up the "additional" memory it needs from the main memory (RAM) of your computer as allocated (available) by the OS (Operating System).
You cannot change that or add directly from somewhere else as this is already the "maximum" encoded in your system's Discrete Logic ( a subsystem hardwired* or etched* on the motherboard ).
One way you can ensure the best total performance of your PC is to install the MAXIMUM amount of RAM that it can take.
The rule on that is determined by two limits:
1) Your OS (32-bit (XP or Vista) will have a limit of 4 GBs (about 3.5 for Windows and 0.5 for the hardware subsystem) and 64-bit (XP or Vista depending on version) can go from 8 to 128 GBs)
2) Your PC slots number and physical RAM acceptance (varies by manufacturer and model line)
* Hardwired means soldered to the motherboard
* Etched means burned on the motherboard ( those gold circuits lines )
The easiest way to get that information is to visit the support site of the PC manufacturer.