What is my usable graphics memory if dedicated memory is 1024 mb and shared memory is 1751 mb?

For most games, usable video ram is 1GB. Period.
The other ram is what Windows can use for its own caching and program use, but that shared ram is of no use to games that require 100% control of the video card.

Since PCI Express slots came out video cards automatically share system RAM as needed. You can't change the setting.

If you have an actual video card (not an integrated chip) then I'd guess it has 1 GB of video memory, but you can double check in other info programs like Speccy or GPU-Z

dedicated memory these days doesnt mean what it used to. if you are told you have some then its more likely to belong to a 2nd gpu or be a cheat to allow older games to run(a lie in other words). in almost all pc's these days the GPU is included as part of the CPU and therefore none of the gpu's have dedicated ram, its all shared. and most 2 gpu systems mean the system is a DUAL gpu system which SHARES the PROCESSING, so for example the HDMI port belongs to the CPU/GPU and the 2nd GPU is just used to manipulate data and the MAIN CPU/GPU handles ALL the actual output. The amount of RAM the GPU gets is a % of what the total is and is preset by the cpu maker with sometimes a small amount of change allowed in the BIOS. the article below discusses the intel settings.

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