When a logo is uploaded to a site via SiteName > Settings, this logo will appear at the top of your site in the designated location per the selected skin. In some cases, you may have uploaded a logo but the logo will appear much smaller on the site than the image that was uploaded and the logo may appear pixelated or "fuzzy".
The size of the logo that is appearing is actually controlled by the skin settings which can be accessed by going to SiteName > Appearance > Customize. In the "Additional Skin Options" section, you will see a field called "Header logo size" and by default the following option will be displayed:
This setting controls the vertical height of the logo that will appear on your site and depending on the size of the logo, it will be scaled proportionately until the logo is displayed at this size. To make the logo appear at your preferred size you can change the number to be a higher value. For example, if the logo should be 125px tall, then you would adjust this to:
Once the setting has been updated, click "Save Skin Settings" via the button at the bottom of the page.