Windows 8 update queries?

So I was gonna buy a new laptop and It comes pre installed with windows 8… So I was planning to update to windows 8.1 first before using it… But I know the update is pretty big and it will take a while to download… So if I install any apps and games like need for speed or battlefield and normal apps like firefox and an antivirus… Will windows uninstall these apps once I finish downloading and install the 8.1 update? Also… How big is the update to windows 8.1? And do you think it's worth updating to windows 8.1 or should I just stick with windows 8 itself… Any help is appreciated…
The lap I'm gonna buy is the lenovo y 510p… If that's at all important…