How to upgrade Win10 system without formatting C drive

According to Microsoft, win10 is able to install win10 directly by upgrading several previous versions, but even if you can't avoid reinstalling the system, how can we keep the data of our C drive when installing the system? The following small series will give you a detailed introduction to the above questions, I hope to be helpful to everyone.

Do not format the C drive to upgrade Win10 method:
The first step, we first download the ISO format Win10 image file, and then extract the file;
the second step, open the unzipped folder, find Double-click to run Setup.exe and follow the prompts. However, it is recommended to try to install Win10 on a local account. After the installation is complete, go to Microsoft users. When installing, select the bottom left corner. "Do not use Microsoft account to log in to the system (not recommended)" ;, do not recommend Microsoft recommended not recommended.
The above is not to format the C drive to upgrade Win10 method, use this method to upgrade, C drive will not be lost.