Reverting to W8.1 from W10 upgrade

[twojays]

Hi all, The reasons for wishing to revert to W8.1 from W10 upgrade (upgraded 2-8-2016) are to numerous to list, suffice it to say, loss of Ethernet, & when slideshow changes to next picture, whatever program you are using fly's to top or start (very annoying), so many updates, etc etc. I bought this HP Pavilion L/T late May 2016, & at the start of activating, was advised to plug in an external media (64 GB flash drive) to make a clean copy of OS, even the BIOS, so that even if PC died, so long as PC had power, I could plug in this flash drive & I could take it back to original factory condition. I hope someone can advise wether this will work, & wether I would need to format the H/D before attempting to do this. Looking forward to answer's, & I wish you all the best for 2017.