Refresh SESSION after change it by submit form

I have code that get me country flag for user when select country from drop down menu like this

    define('WCDP_PATH_INCLUDES', dirname(__FILE__) . '/inc');

    if (!class_exists('GeoIP')) {
    include(WCDP_PATH_INCLUDES . "/geoip.inc");
    }
    $geo_data = geoip_open(WCDP_PATH_INCLUDES . "/GeoIP.dat", GEOIP_STANDARD);

    $country_code = geoip_country_code_by_addr($geo_data, $_SERVER['REMOTE_ADDR']);

    $countrynameselect =  $_SESSION['countryname'];
    if ($countrynameselect){
        $country_code = $countrynameselect;
    } else {
        $country_code = geoip_country_code_by_addr($geo_data, $_SERVER['REMOTE_ADDR']);
    }       
    // Build HTML for flag icons.
   ?>

   <img src="<? bloginfo('stylesheet_directory')?>/flags/sm/<?php echo strtolower($country_code).'.png'; ?>" border="0" style="margin-top:10px" id="flagc" />

Now when user select country from drop down menu, i save country post in SESSION, But when user change agin, itsh not update SESSION, and to update it, we must refresh page to shpw new SESSION value.

What can i do ??