If you need to choose another font in theme, you can use theme option – font option OR add external custom fonts
But what if you want to disable totally default font of theme (Roboto). Here code snippet for functions.php
add_action( 'wp_enqueue_scripts', 'dequeue_default_theme_font', 100 );
function dequeue_default_theme_font() {
wp_dequeue_style( 'default_font' );
}