Make an image of the current installation:
Best approach:
install all available updates for all programs: including video drivers
reboot, check for updates, reboot
Run the w8 advisor: uninstall any programs identified as problems
download updated versions of programs and drivers
run system restore to create a full restore point: windows updates do not always do this
run disk clean-up, delete system restore files: this deletes all but the most current point
stop the hibernate file, and the page file: reboot
defrag, at least 5 times: I use the windows defragger, alternating with auslogic (system files moved to front of drive )
Create an image of the OS disk to an external disk, create the repair disk
Start the pagefile, system managed
Now run the upgrade: from the ISO disk created during the download process: imperitive to create the disk
If all does not go well: restore the image and start again
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Deleting the system restore files, the pagefile, and the hibernate file always significantly reduces the size of the image file, and hence the time to create/restore.
Alternative: restore the image to a new disk in the same machine and upgrade it.