I looked at TwentyThirteen’s twentythirteen_fonts_url()
function and there are no hooks so you need to
deregister twentythirteen-fonts
and enqueue your own fonts.
Removing the fonts is easy:
function deregister_gfonts_wpse_111190() {
wp_deregister_style('twentythirteen-fonts');
}
add_action('wp_enqueue_scripts','deregister_gfonts_wpse_111190',100);
Add your own Google fonts (or other) the same way that TwentyThirteen did.
You will need to add another stylesheet to override the places where TwentyThirteen uses the fonts though.