Get yourself a large USB drive or a network location with enough room to store the image and run the command below from PowerShell started as Administrator
wbAdmin start backup -backupTarget:D: -include:C: -allcritical -quiet
Make sure you change the drive letter of the backup target from D: to the letter for your drive letter prior to running the command. What this does is simple. It executes Windows Backup (since Microsoft removed the GUI interface for it in Windows 8/8/1) and runs a full backup for you.
If you want to save your backup to a network location this is the command
wbAdmin start backup -backupTarget:\\sharedfolder\foldername -user:username -password:userpassword -include:C: -allCritical -quiet
This will kick off the same backup process as above and send it to your network storage instead.
Once the backup completes you can browse the backup location and you'll find some very familiar folders. The old WindowsImageBackup folder, the .xml and .vhd files that were used in the Windows 7 backup and restore feature.
That's all there is to it. I wish you luck with your Windows 10 upgrade.