Seems like HP has made your vRAM amount permanent since there is no BIOS Settings to increase the vRAM.
Windows will use whatever System RAM is needed to run any programs or games by the Integrated Graphics. Having more vRAM might make the Integrated Graphics more efficient in doing its job.
vRAM can only be changed in BIOS and not through any tweaks in Windows. Possibly HP could come out with a newer BIOS version that does have a setting for increasing the Integrated vRAM. Otherwise you will just have to accept the amount of vRAM that came with your laptop.
I would open a HP Support ticket and ask them directly. It is possible you missed or misread the BIOS Setting to increase vRAM. If you didn't then HP Support might be able to tell you if they will have that option in the future via a BIOS update or not.