this is in fact the update that windows 8 has, it adds back a sort of start menu, and they claim it largely un-breaks windows 8, however, i tried it, and it rendered my computer near unusable, well over 50% of the programs i tried to use, that worked on windows 8, no longer worked on 8.1. i would personally avoid this update like the plague it is, in order to remove it, i had to do a factory restore, and even that nearly got screwed up because one part of 8.1 update is, it adds 8.1 to your factory backups thus making it where you cannot go back to windows 8. thankfully i spotted that setting and told it no or i would have been screwed.
sadly there really isnt a way to get it to go away, after the first time that it tries to download it should give you a new option one of those being to do it later, or skip it, something like that, and about twice a month it will ask again, and you should be able to just skip or tell it later.
now i will admit that i play games, and largely none of them worked, so my over 50% program failure did include that, but it also had photo editing software that would run in 8 even if it had to be ran in compatibility mode, that would not run in 8.1 for anything.
your experience might vary, and you might really like it, personally i wont upgrade to 8.1 again, and use start 8 and modern mix to restore a windows 7 feel to 8 making it far more user friendly.