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I understand that you would like to increase the dedicated video memory. I would like to help you.
The Graphics Processing Unit (GPU ) does not have a dedicated memory. As you were saying, it uses shared memory that will be allocated automatically depending on various factors.
What you need to keep in mind is that the maximum amount of graphics memory depends on the available system memory, BIOS, and system settings. However, your computer seems to be using the maximum amount of shared memory. Please check the table under the following section: What is the maximum amount of graphics memory or video memory my computer can use in Windows 10? > Intel® HD Graphics 5000/4600/4400/4200
In addition, computer manufacturers can add customizations and make changes that may limit or reduce the graphics memory reported by your system. You may be able to change the amount of graphics memory from the BIOS, but you need to check if the settings is available for you to modify it and probably get support from your system manufacturer.