I just want to share what I did when I couldn't do an upgrade but didn't want to re-install 1000 programs and re-configure everything:
Clone your old Windows 8 disk (or Windows 7).
Install fresh copy of Win10 on the new drive, but without wiping the disk first.
Call your new user "Temporary" or something similar during setup. You'll only use it briefly before you are back with your old user from the previous version of Windows.
Log out from normal user and log in as local Administrator.
Copy over Program Files, Program Files (x86), ProgramData and your old User profile from the old Windows disk, to their respective location.
Set up a new User account with the same user name as you had before.
Log in as this user. A new profile will be created. Log out again and in as Admin.
Delete the newly created user file for your preferred user account.
Go into the registry and locate the Profilelist key (this is documented elsewhere). Point the profile to your old User folder which you copied over to the new installation. Log out from the Admin account and try logging in as your old user. This may not work the first time. Windows may either just ignore the command or give an error message. But don't panic. It can absolutely work, you just have to gradually copy the content of the Appdata folder one folder at a time. Go back to the User folder that Windows had just created for that user - the generic profile. Start by replacing everything apart from the AppData folder and check that you can log in. Should be fine. Then replace folder by folder starting with the LowLocal, then Roaming and finally Local which is the trickiest. The folder that's most likely to create problems is the Microsoft folder in the Local folder in Appdata. The more you an copy over from your old user profile the more work you save yourself with the installation and configuration of Windows.
Eventually you will be able to log in with that account, using your old profile. A lot of things will look familiar if you had customised your old profiles.
Also, the programs that you copied over will be indexed by Windows 10. A surprisingly large number of them will stil work even though they weren't installed at that machine. But they use only the files in their own installation directories and can run without any added registry entries. Obviously if they were default for opening som file type, that will have to be re-set. But the programs themselves for the most part will still work.
Examples of programs that continue to work are Google Earth, Firefox, inluding customisations, Chrome, Mirc, Aomei, Qbittorrent, Thunderbird, Media Player Classic, VLC, Audacity
More complex programs will not work anymore. For instance, Office, Adobe products, Itunes, Logitech Setpoint, OpenVPN.
Many things like for instance scripts that you may have written as a scheduled event will continue to work.
Some programs may lose their licensing and you may need to enter license info for a few programs.