How to increase video memory on bootcamp?

I have been using Windows 10 bootcamp for awhile now and it works perfectly except for the amount of video memory used. How can I increase the video memory from 256 mb without paying for anything and if needs be what would be the best thing to do? External gpu? Thanks and specs below

2017 MacBook Pro 13 in. Four Thunderbolt 3 Ports

3.5 GHz Dual-Core I7

16 GB 2133 MHz

Intel Iris Plus Graphics 650 1536 MB