You can change the font style by the css code below:
.main blockquote{ font-family:'……'; /*add the font style by yourself*/ }
If you want to use fontface or google font, you need add the code in 'Symplex->FontFace' or 'Symplex->Google Font', or you can add it in 'Symplex->Custom'.
Please make sure the font file has already in your server and has been enabled.