Before I explaine how to upgrade phpmyadmin in Xampp for Windows®, here are some brief about PhpMyAdmin.
What is PhpMyAdmin?
"phpMyAdmin is a free software tool written in PHP intended to handle the administration of MySQL over the World Wide Web. phpMyAdmin supports a wide range of operations with MySQL. The most frequently used operations are supported by the user interface (managing databases, tables, fields, relations, indexes, users, permissions, etc), while you still have the ability to directly execute any SQL statement.
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phpMyAdmin comes with a wide range of documentation and users are welcome to update our wiki pages to share ideas and howtos for various operations. The phpMyAdmin team will try to help you if you face any problem, you can use variety of support channels to get help."
Complete Description, read here http://www.phpmyadmin.net/home_page/index.php
The first thing you must to do is download PhpMyAdmin script in phpmyadmin.net, then extract them to folder C:\xampp (Xampp Installation folder). But before start, first you must rename old phpmyadmin folder for backup in case of error in new phpmyadmin script.
When finished copying all the files, now to do is copy 2 configuration files in old phpmyadmin folder to the new folder. The file is config.inc.php and config.inc.php.safe.
When finished copying the files then it's time to try PhpMyAdmin v3.4.0. And the result is really great, the login page and the PhpMmyAdmin dashboard now looks more elegant.Here are some screenshots of PhpMyAdmin v3.4.0 in Xampp v1.7.4-VC6 for Windows.