If you want to change  default username and/or password of your xampp for any reason like my one(Using different mySql already installed in my machine ).  You simply do the following.

1. Open phpMyAdmin’s config file. In my case I’am using xampp-1.7.4 the config file named config.inc.php in ../xampp/phpMyAdmin/.

2. Check if $cfg[‘Servers’][$i][‘auth_type’] = ‘config’ if it’s not ‘config’ but ‘cookie’ or ‘http’  then you need to create a new MySQL user account before you change those(username and password) values.

3. Now change the value of $cfg[‘Servers’][$i][‘user’]  and $cfg[‘Servers’][$i][‘password’].

Good luck with that.