Zurb Foundation SASS

hello i am learning zurb-foundation, responsive framework. i want to know that how can i edit the default values of the SASS variables. i searched over internet but due didn’t found anything.

http://foundation.zurb.com/docs/components/top-bar.html

Under Available SCSS Variables section, SCSS variables are provided but i don’t know where to place them after altering the value.
as foundation is not much older, not much help is available over google.

Thanks

The settings are included within a config file https://github.com/zurb/foundation/blob/master/templates/project/scss/_settings.scss, they come standard with a full gem install which you can find here http://foundation.zurb.com/docs/sass.html