When the Win10 Upgrade first came out, lots of folks with Win7 PC (me, included!) ran into the problem where the Upgrade failed on trying to update the System Reserved partition, because it was only 100MB, when Win10 needed a partition that was 350MB. We solved the problem by resizing that partition.
What is odd about your situation is that the original Upgrade worked, but NOW, it's complaining about that partition.
Once you have that, look at your partitions to see what is adjacent to the 100MB partition. It is usually the OS partition. Then, resize that to remove 150MB from it to leave room to grow the system reserved partition. You will probably have to reboot to make this change. Once that is done, grow the system reserved partition to fill the new space.
Once that partition is 250MB, then retry the Win10 Update.
***If my post helped, click the thumbs-up symbol to say thanks***
***Please mark Accept As Solution if my post solved your problem***
I am a volunteer and I do not work for, nor represent, HP