If you’ve made customizations then you should just update it manually since (as mentioned by StudioPress) there is no easy way to update a customized version of a css file with a brand new css file….since everything will be different. The Epik widget names and classes will be the exact same as the original, but it’s the Genesis 2.0 markup code that will be different. If you made no changes to your theme and updated/replaced this with the newer version then it would work fine. It’s only if you’ve made customizations that you would need to manually make changes.
He is developing this on top of the latest Genesis Sample Child theme (from scratch) so it only has the HTML5 code and not the old code. Keep in mind, if you choose not to update your files to 2.0/HTML5 your site will still work fine.
Take a look at some of the Genesis converters which automatically do all of the work for you – https://www.google.com/search?q=genesis+2.0+converter …of course you’ll need to backup and save your old files just in case.
Here is someone that did it with the Epik theme – http://wpsites.net/wordpress-themes/how-to-convert-your-studiopress-child-theme-from-xhtml-to-html-5/ There should be many more tutorials in that Google Search link above.
I create awesome sites for awesome people! Contact me if interested – ericsanchez1585@gmail.com