There are two different ways to change the logo in a template. You can either use your own unique logo or customize the existing logo with your own company name and tag line.

Use your own unique logo

1. Go to the 'Module Manager' found in the Joomla! Administrator
2. Click 'New'
3. Select 'Custom HTML'
4. Enter a descriptive title such as 'My custom logo'
5. Select 'Show Title': 'No'
6. Select 'Position': 'Logo'
7. Use the text editor to select an image from your server by clicking on the 'Image' button just below the editor. (If there are no images on your server yet, you can upload one at the bottom of the dialog window that pops up.)
8. Hit 'Insert' in the dialog window after selecting the image you want to use as your logo
9. The image should now appear in the text editor
10. Hit 'Save' and your custom logo will appear on the website as your logo!

Customize the existing logo

1. Go to the 'Template Manager' found in the Joomla! Administrator
2. Click on the name of the template style you want to customize the logo for
3. Look for the section 'Logo Settings' on the right side of the screen
4. Use the available parameters to customize the logo
5. Hit 'Save' and your customized logo will appear on the website!