There are 2 ways to go on about updating Windows to a newer version while keeping user data:
''RECOMMENDED FOR MULTIPLE PCS'': You can install the Windows 10 ISO from Microsoft's website, flash it on a thumb drive, plug it in while the OS is running, then run setup.exe, it will guide you on how to keep everything. ( i suggested a thumb drive because i am assuming you are gonna do this on multiple PCs)
''RECOMMENDED FOR A SINGLE PC:'' You can just download the Windows 10 ISO, open it in explorer to mount it, then run setup.exe, should be business as usual.
NOTE:You ***can't*** update PCs without having the OS running, booting the ISO is exclusively for new installs.