Hi,
If you do not like Windows 10, there is inbuilt provision in Windows 10 for you to rollback to the previous Operating System within the first 30 days.
"You have a month to downgrade to Windows 8.1 or 7, depending what you upgraded from, if Windows 10 isn't right for you"
http://www.techradar.com/au/news/software/operating-systems/you-have-a-month-to-downgrade-to-windows-8-1-if-windows-10-isn-t-right-for-you-1299430
"Going back to Windows 7 or Windows 8.1"
http://windows.microsoft.com/en-gb/windows-10/going-back-to-windows-7-or-windows-81
If you fail to do so within the first 30 days of upgrading that option will be removed and, you will either have to reinstall the original Operating System from the original Media, or from a System Image that you made of the original Operating System before
doing the Upgrade to Windows 10.
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Or you may have to follow these Methods to reinstall windows 8.1.
You can contact the Laptop/Computer manufacturer and order Recovery Media from them for a small cost.
Or create your own Recovery Media to do a clean install of Windows 8.1.
"Create installation media for Windows 8.1"
http://windows.microsoft.com/en-us/windows-8/create-reset-refresh-media
A similar Tutorial which may also assist you
"Create Installation Media for Windows 8.1"
http://winsupersite.com/windows-8/create-installation-media-windows-81
In the first screen of this very simple wizard, you need to choose the following:
Language. English – en-us if you're in the United States.
Edition. Windows 8.1 (Core), Windows 8.1 N, Windows 8.1 Pro, Windows 8.1 Pro N, or Windows 8.1 Single Language.
Architecture. 64-bit (x64 ) or 32-bit (x86).
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"How to Create a Bootable USB or DVD with a Windows 8 or 8.1 ISO"
http://www.eightforums.com/tutorials/2227-create-bootable-usb-dvd-windows-8-iso.html
Warning
This will not work to install Windows 8 or 8.1 for UEFI. For that, see this tutorial below instead.
UEFI Bootable USB Flash Drive - Create in Windows
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How to clean install:
"How to Do a Clean Install of Windows 8 or Windows 8.1"
http://www.eightforums.com/tutorials/2299-clean-install-windows-8-a.html
Cheers.