This message was posted on behalf of Intel Corporation
I understand you have installed 4GB of memory under Windows® 10 32 bit and the computer can use 1.92GB.
This is an expected behavior since your are running Windows® 10 32 bit due to addressable memory information you will find at the product specification page
You can bypass this memory limitation if you would have Windows® 10 64 bit.
I tried this on a GY NUC which is the same as the PY Pentium NUC only it has 32GB of eMMC on-board and comes with Windows 10 Home x64. You don't see the same 2GB reserved ram as you do on the 32bit version.
This may be why the PY NUC does not support 32bit Windows. Unless there is a reason you have to have the 32bit version, I would go with 64bit as you will have access to almost all of the 4GB of ram in Windows.