Partitioning problem

My personal laptop has a 1TB spinning drive. I bought the laptop new
over six years ago. It was, then, fast, with a quad core i7, and 8 GB
RAM. The HD came with three partitions:

1 the emergency partition, under 50 GB with the emergency boot files
2 the OS boot partition, 390 GB, with Win 7 Pro. (I upgraded it to Ultimate)
3 the data partition, about 500 GB, no OS.

When I upgraded to Win 8, I did it by installing cloning over the OS
partition to the data partition and upgrading the data partition. I did
that just in case I didn't like Win 8. I didn't like Win 8 and went back
to using Win 7 for most things, though I left Win 8 on the old data
partition.

When I upgraded to Win 8.1, I did the upgrade on the Win 8 partition. I
still spent most of my time with Win 7.

When I upgraded to Win 10, I again did the upgrade on the Win 8.1
partition. I am currently spending most of the time in Win 10. In fact,
I am spending so little time in Win 7 that I decided that I wanted to
kill the Win 7 partition, recover the space, and add it to the Win 10
partition.

Problem: Disk Management shows the Win 7 partition as being an active,
system, partition. The Win 10 partition is also active, and is the boot
partition, and where the page file lives. Because the Win 7 partition is
the active system partition, Disk Management (and everything else I've
tried) won't delete that partition, and I suspect that if I managed to
do that then there might be problems, as there is very likely a reason
why Windows thinks that it is a system partition.

So how do I make the Win 7 partition NOT a system partition? Would the
solution be as simple as cloning the Win 10 partition over to the Win 7
partition (there should be enough space for everything) and then booting
from the other partition and killing the current Win 10 partition? I
doubt it. I can see where BCD might get confused if I did that, just for
starters. Do I have to go as far as getting a new drive (spinning or
SSD) and setting up the emergency volume and just the Win 10 partition
on it? This laptop is getting elderly, and I might get an SSD to extend
its life, but other than that I'd get a new laptop and probably just
clone the Win 10 partition over. I originally cloned the Win 7 partition
using Laplink PCMover, and I still have the installer for the old Win 7
version. It's 5+ years old now, and may not necessarily work with Win
10, and besides there may be licensing issues as it was purchased to be
used in a Win 7 environment. I suspect that a support cal into Laplink
at this late date would not be well-received.