The code I found... $('.sidebar_btn').css('background-image', 'url(images/x.png)');

My question is how change x.png for the new image

Take any fitting image, pop it into the images folder and change this bit of the code: url(images/x.png) to the new image name, like e.g. url:(images/myown.png) or if your image is a jpg one then url:(images/myown.jpg).