replace windows 8 with fedora 21

I'd back up first in case something went wrong. Recovery disks are always a good idea. 'Advisable' is opinion based, but far too many people linux, then panic when they want to go back.

I didn't need to disable secure boot - fedora has a signed bootloader and it just works. I did use a installer USB made with liveusbcreator, and I believe it installed in UEFI mode.