As you probably know Microsoft have put a lot of hours into getting the Windows upgrade process to work from Windows 7 and Windows 8.1.
The computers I have tested on I haven’t had any issues with the upgrade, but there are some things you have to consider that will not work. Among things that will not work are:
On the other hand you have no dependencies to ADK, it’s a lot faster, there is built-in rollback if something goes wrong to get the user back to previous operating system exactly where he was.
When the upgrade is completed you will notice that there are some folder left in the root: $Windows.~BT and Windows.Old
These files and folders will be automatically deleted after about 30 days.
How do we clean-up these? The manual step is to run the Disk Cleanup tool elevated as Administrator
and check Previous Windows installation(s)
another option is to run DISM
Dism.exe /online /Cleanup-Image /StartComponentCleanup
How does the 30 days grace period work? There is a scheduled task that will take care about this. The task is StartComponentCleanup, this will regularly clean up and delete components that are not in use and it is trigged by the operating system. The task will wait at least 30 days after an updated component has been installed before starting clean up of the old versions.
You can trigger this scheduled task with this command
schtasks.exe /Run /TN “\Microsoft\Windows\Servicing\StartComponentCleanup”
Always I try to add a reference: https://technet.microsoft.com/en-us/library/dn251565.aspx