Dedicated memory falls under the umbrella of Hardware Reserved, which in this case is a portion of RAM that the BIOS has allocated to the graphics for its exclusive use. This amount may, or may not, be able to be changed if the BIOS permits. If this option isn't there, then you're stuck with the default. Shared memory, and this depends on the amount of memory in your system, is dynamically assigned as and when required. However, as more memory is assigned to the graphics, it means that less is available for other uses and the reliance on the paging file will increase, together with a general slowing down of your machine.
Unfortunately, there isn't a great deal you can do. Laptops just simply are not designed for heavy graphics applications such as games; rather they are intended as business/office type machines where there is less graphics demand. That is not to say that they won't run games; they will, but it won't be as smooth as on a desktop.