Personal Logo not displaying on coolwater theme

Hello, my question today is: how can I put my personal logo on page header? I'm working on Cool water theme, and although I put the path for my logo image file into the configuration settings, it won't come out: there's only the indication of my site's address. Do I have to change something into the file page.tpl.php? Add a string of code maybe? can someone tell me where to put it, if I have to, and what to write? thank you as usual for your kindness!!!!