How can i change the background image

I have installed the program on my PC and tried to make some customized changes, like change the background image.

Here is where i tried: “Module and Application Builder” - “set up” -“Display” -“Background Image”. After choosing the image file and click “save”, the background image of the interface remains the default color of background color, #ffffff, and the uploaded image wasn’t displayed. I tried to change the color to transparent but failed.

Can anyone here tell me how to change the background image to designated one?

Thanks in advance!