Can I change my hardware after upgrading to Windows 10 from a previous Operating System?

This depends on the license you had with your original purchase of Windows.

Retail License

The license will be treated as Retail so you can physically change your computer's hardware. If there is going to be a significant hardware changes, you will first need to un-register your Windows 10 license before the new hardware is installed.

OEM License

No, it is not to carry out a significant hardware upgrade on your machine if your previous Operating System held an OEM license.