To change the website font(s) you need to modify the theme's CSS. In case of Snow Flat that's the file qa-theme/SnowFlat/qa-styles.css in your Q2A directory. Add your desired font to the font-family properties in that file.
Note, however, that CSS normally expects fonts to be installed on the client computers (that's why you're putting a list of desired fonts with a generic font like "sans-serif" as fallback). If you want to use a custom font on your website you'll have to make that available to the clients. The usual way to do that is to create a web font (in the Web Open Font Format), put the .woff file(s) in your Q2A install directory, and reference them in the CSS like this:
@font-face {
font-family: Foobar;
src: url('/somefont.woff');
}
body {
font-family: "Foobar", "Ubuntu", "Helvetica", "Arial", "FreeSans", sans-serif;
}
Beware, though, that fonts are oftentimes copyrighted, so you need to make sure you're actually allowed to (re-)publish a font if you want to put it on your website (lest you may face legal action from the copyright holder).
