I should have said this earlier: Before making any changes, be sure that you have a current backup of anything you need on the laptop. Double and triple checking is not wrong.

ChromeOS (the PC to Chromebook option) is a good choice and it’s rare to see them get compromised.

Upgrading to Win10, if your hardware supports it, is a good option. I’ve had mixed results with the free upgrade tool of late.

If you choose Linux, you may have some learning to do. I’d suggest you pick a distribution that’s easy to use — this article seems to give good advice: https://itsfoss.com/best-linux-beginners/.

I do not recommend dual boot to Win7 — instead I’d recommend backing up all the files you need twice and then copying them back onto the laptop after whatever change you make. Why twice? Well, let’s just say that “chaosmagnet” long predates my time here on ETS, and I don’t think there’s a way to break a PC or lose data that I haven’t seen (or caused!).

If you need access to data that can only be read by a Windows application and cannot upgrade to Win10 in place, you should probably consider buying a new laptop with Win10.