My main question right now is how to proceed to do two things:
1. Wipe out everything not needed
2. But keep the Win10 OS intact

Here is a picture of the new (to me) Windows 10 desktop.
https://s27.postimg.org/udef4ncoz/image.gif

This post is just to explain the specifications as I know them to be.

Windows 10 Pro version 1511
(but the sticker says Windows 7 Home Premium OA 64 bit)

HP Pavilion Model P6230Y. AMD Phenom II 810. 16GB RAM, 930GB HDD
ATI Radeon HD 4200

There is only one user but the 930GB HDD only has 380GB space left.
I don't want any of her stuff but I want to be careful what I delete.

What I really want to do is wipe everything out and start over but I don't
want to lose the existing Windows 10 license.

At the moment, I created a new user (which you see in the photo as it took
a long time on the first login for some reason).

The only odd thing, so far, is that I can't find the Wi-Fi settings because
this computer was apparently always on the Ethernet whereas for me it will
likely be on Wi-Fi so it hasn't been on the net yet.

Since I loved Windows XP, and I since skipped Windows 7, 8, and 9 (or
whatever the versions were), I will have a steep learning curve (I can tell
already by clicking about).

The main question right now is how best to proceed to get rid of all the
stuff from the previous owner WITHOUT destroying the Windows 10 license?