I was on Win 7 and did the Win 10 upgrade. A few days later I wanted to do a clean install with Win 10 install on a DVD I created. I have 2 internal drives. To protect my data on drive D I disabled it while in boot mode but accidentally disabled C instead. That caused me to install Win 10 on the D drive but luckily for me I still have my other data and hence not a clean install either. No reformatting of the drive.

How do I uninstalled Win 10 on my D drive without losing my other data so I can start over and which drive should I boot from to do that? I don't need to roll back to a prior version of Windows.

I haven't verified this but if I boot from either of the drives, that drive becomes the default C drive.