Hello,

The data/content that you have added in the free version of the theme will work fine even when you update the theme from free to pro.

However, the settings that you previously specified in the customizer of the theme will no longer be there as in pro version of the theme, you will get a fresh customizer and you should setup the settings manually.

Alternately, you can also add the given snippet below in the child theme of your pro theme which will get the customizer setting that you specified in the free theme.

function mezze_pro_child_customizer_options_import() {

if ( get_stylesheet() !== get_template() ) {
   add_filter( 'pre_update_option_theme_mods_' . get_stylesheet(), function ( $value, $old_value ) {
        update_option( 'theme_mods_' . get_template(), $value );
        return $old_value; // prevent update to child theme mods
   }, 10, 2 );
   add_filter( 'pre_option_theme_mods_' . get_stylesheet(), function ( $default ) {
       return get_option( 'theme_mods_' . get_template(), $default );
   } );
}

}

add_action('init', 'mezze_pro_child_customizer_options_import'); 

Hope this helps,

For any further query/confusion, feel free to write us back,

Regards!!