How to delete old windows 10
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As long as you have no plans to roll back to a previous version
you can delete using Disk Cleanup. (:
How to recover/restore your previous version of Windows
using the Rollback feature:
http://answers.microsoft.com/en-us/insider/wiki/insider_wintp-insider_install/how-to-recover-restore-your-previous-version-of/76b6750c-5bb2-40bc-a7e3-f03cec62338b
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