Magento

Hello, I wanna change ‘Default welcome msg’ and logo name in the header. 
I found and change config.xml (app\code\core\Mage\page\etc\config.xml) and line 85 <welcome>welcome guest <welcome> and line 83 <logo_src> images/mylogo.jpg<logo_src>
but it not work. The old logo and ‘Default welcome msg!’ are still in there and I try delete this config.xml file still show old logo and ‘Default welcome msg!’ !! I’m confusion~~

after that I go to change header.php(code\core\Mage\Page\Block\Html\header.php) line 63: $this->_data[’welcome’] = ‘welcome guest’ , Now wok. 
But I don’t wanna change php file.

Anyone can help me?  how can I find that right XML file??
Thanks a lot..  sorry for my English

You dont need to deal with the xml file for this at all.. in order to change the “default welcome msg!” just go to CONFIGURATION > SYSTEM > (SELECT YOUR STORE) > DESIGN. and change the values under HEADER. and you are all set.

hope that helps you out.