I am using Zurb\'s Foundation framework, and I would like to know how I can edit the default values of the SASS variables. I searched all over the internet but I was not able to
You should be looking into Sass that is already explained on their site and can be found here. I suggest you start reading the documentations for V3, Foundation 3, as those docs explain better how you can harness the power of Sass with Foundation. You can start reading here then do further reading here. Honestly, Zurb does a fantastic job of documenting their Foundation framework and all you need to know, 99% if not all, are already on their documentation pages.