#################### update function ############################
function sb_update_plugin(){ //runs when all plugins are loaded (needs to be deleted after register_update_hook is avaiable)
    global $wpdb, $sb_ip_log;

    if(sb_get_plugin_version() != get_option('sb_plugin_version') OR get_option('sb_plugin_version') == FALSE){
        add_action('admin_notices', 'sb_activation_notice'); //show activation message

        sb_create_db_table(); //update the plugin table to a desired structure

            #### now comes everything what must be changed in the new version

            if(get_option('sb_plugin_version') == '1.3'){ //upgrade to v1.4:
                add_option('sb_automatic_ip_address_duplication', '0', '', 'yes');
                add_option('sb_automatic_ip_address_duplication_recurrence', 'twicedaily', '', 'yes');
                add_option('sb_spam_comment_automatic_elimination', '1', '', 'yes');
                add_option('sb_automatic_ip_address_duplication_last_cron_run_time', '', '', 'yes');

                //renaming options and values -- v1.5 - zpetna kompatibilita
                add_option('sb_access_restrictions', '1', '', 'yes'); //adding new option
                delete_option('sb_detection_of_spammers_cookies');
                add_option('sb_detection_of_spammers_method', '1', '', 'yes');

                delete_option('sb_detection_of_spammers_time');
                add_option('sb_detection_of_spammers_time', '2592000', '', 'yes');
            }

            if(get_option('sb_plugin_version') == '1.4'){ //upgrade to v1.5
                add_option('sb_access_restrictions', '1', '', 'yes'); //adding new option

                //renaming options and values
                delete_option('sb_detection_of_spammers_cookies');
                add_option('sb_detection_of_spammers_method', '1', '', 'yes');

                delete_option('sb_detection_of_spammers_time');
                add_option('sb_detection_of_spammers_time', '2592000', '', 'yes');

                //add new column hits to sb_ip_log table
                $wpdb->query("ALTER TABLE $sb_ip_log ADD hits INT;");
                //add 1 to all rows
                $wpdb->query("UPDATE $sb_ip_log SET hits = '1';");
            }

            #### -/changes

        update_option('sb_plugin_version', sb_get_plugin_version(), '', 'yes'); //update plugin version in DB
    }
}