Hi there
When you install windows 8.1 from the ISO using a currently running version of Windows 8 (mount iso as a virtual DVD and run setup.exe) choose KEEP NONE at the prompt to clean install but DO NOT DELETE the WINDOWS.OLD file (will be located in the C drive) immediately.
Some of your drivers might not be found at Windows 8.1 install but if you use the control panel and select update...
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