Hi Ahsan, the amount of memory used for graphics may be a fixed amount or may vary up to a maximum. In the end it depends how this was implemented by your computer manufacturer.
For your graphics processor this amount can go up to 1.7 GB which is allocated from the RAM, not the storage memory. I recommend reading the following article for more information: Graphics — Graphics Memory FAQ For Microsoft Windows 8 and 8.1*
Based on the link shared by Joe, the graphics controller in your system can go up to that amount of Video memory the system can handle or take but it does not necessarily means it will reach that since depends on many things such as the game settings, and system resources.
It is important to say that video memory will sure help on video performance but the most important thing is video processing which is directly on the graphics controller. You may find that the system can run certain heavy games and others depending on the game settings may not run.
Here you can find a list of tested games with your controller: