30 days then you can
http://betanews.com/2015/08/17/how-to-uninstall-windows-10-and-go-back-to-windows-7-or-8-1/
I decided to give the free upgrade to Win 10 Pro 64-bit a try, and never realized the level of misery I would encounter: a) Search box doesn't work; b) Start menu is broken; c) Can't add user accounts; d) Edge browser is a cruel hoax. As a result, I'm done with Win 10 and plan to go back to Win 8.1 Pro 64-bit which has been a remarkable OS in many key ways. Please advise on the best way to accomplish this. Thanks, as always, for your support.

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