As you start to customize your newly installed Magento 1.8, you’ll probably want to change the logo that displays in the top right section of the header on each page. This can be easily accomplished in the Magento 1.8 Admin Panel at any time.
Uploading your logo to Magento
Step 1 : With your FTP program (in this example we’ll use FileZilla), go to the root folder of Magento.
Step 2 : Go to skin/frontend/default.
Step 3 : From here you’ll need to select the template you are using. Currently we’re using the “modern” template so we’ll click on that folder.
Step 4 : Now, click on the images folder.
Step 5 : Select the logo file, and upload the file.
Setting the path to the logo in Magento
Step 1 : Log into your Magento Admin Panel
Step 2 : Go to System ->> Configuration
Step 3 : Click on “Design” in the left side menu pane
Step 4 : Open the “Header” section
Step 5 : Change the file name in the “Logo Image Src” to the file name you just uplaoded. Leave the images/prefix alone
Step 6 : Click “Save Config”