Check and see which version of windows 8.1 that you installed, 86x(32 bit) or 64x(64bit), most core i7 pc use 64bit windows, i will also recommend you download a new video drivers for you pc.
This happened to me on my Alienware dell laptop, i went to dell support and downloaded new video, chipset and bios drivers for windows 8, after installation and system restart it was back to 128mb, am not quiet sure which driver did the trick doe, but these are the 3 i downloaded
Mostly windows 8.1 will not have pre-installed drivers for your laptop and you need to download from the apporate site. Go to http://support.toshiba.com/drivers
and get new windows 8.1 drivers for you pc, when you arrive at the site, do the following
1. Enter your model or serial number? in space provided and hit Go
2, Now select drivers for windows 8 and download. Make sure you download video, chipset and bios drivers.
3. Install the drivers after download and restart your laptop.
*Core i7 computer/laptops are very fast regardless of the dedicated memory allocated to it, it will still play most games and do things you require your computer to do. so you can choose to ignore it and use you computer
*Be careful when installing the bios update as it can brick(spoil) you laptop and render it useless..
* If you video card in NVIDIA, then you can avoid all the above trouble and use turbocache to restore your dedicated memory back. see more details here http://www.nvidia.com/page/turbocache