Royal Slider full width

I’m trying to get the royal slider in full width on this site: kittyvandenakker.nl
but i can’t figure out where to put these codes…

http://help.dimsemenov.com/kb/royalslider-jquery-plugin-faq/how-stretch-slider-to-full-browser-width-and-height

i’m not a web developer so please explain it in terms so simple that any idiot can understand.