Environment: SCCM 2012 R2 1511, Windows 10 ISO file, Windows 7 to be migrated.
Add the Windows 10 iso file as a Operating System Upgrade Package.
Select the files where your Windows 10 is placed.
Distribute the content to the Distributions Points
Create a Task Sequence and select the ” Upgrade an Operating System from upgrade package”
Browse the Operating System upgrade package
Do not install any software updates.
Finish the Task Sequence.
Create a Device Collection and place there the target macchine.
Create a Deploy of the Task Sequence, and select the Collection created in the step before.
Just wait for the deployment and review smsts.log to avoid any errors.
All these steps are extracted from the following sites: