You can replace the Yurbi with your own by adding an entry to the CustomJS file on the Yurbi server. By placing it there, you don't have to worry about the change being overwritten when you apply upgrades to Yurbi.
Go to c:\program files(x86)\yurbi\frontend\assets\js\lib directory and you will find the custom.js file.
To replace the logo in the header of Yurbi, add this line of code to the doHeader section:
$("header .navigation .logo").find("img").attr("src", "assets/images/yourlogo.png");
Per the relative path above, be sure to place your logo in this directory c:\program files (x86)\frontend\assets\images\
To replace the logo on the login page of Yurbi, add this line of code to the doLogin section:
$(".login header a img").attr("src", "assets/images/yourlogo.png");
After saving the file, go to your Yurbi site to test the changes. You may have to hit refresh or clear the cache to see the updates.
Depending on the background color of your logo, you may have to also adjust Yurbi colors or your logo size to fit properly. The default header logo is 80 x62 and the default login page logo is 165 X 60.