To change the background of FL Studio 11, you will do the following:
Open FL Studio -> View -> Background -> Set bitmap wallpaper..

How Can I Change the Background Image of FL Studio?

Before, changing the background image was actually really simple!

Double click in behind FL Studio and a window will pop up, allowing you to change to what ever image you please.

Changes in FL Studio 11,

FL Studio - Changing Your Background - Steps

Since the update of FL Studio 11, the double click of the background hasn’t been working for me, so I had to find another route.

It was just a matter of going to the VIEW options at the top of FL Studio.

This leaves you working in a more enjoyable environment, plus, it’s always nice to see a brand you are trying to create while working/beat making!

To break down those steps:

Open FL Studio -> View -> Background -> Set bitmap wallpaper..

On a side note, if you are creating tutorials, or putting out beatmaking videos, this is a way for free branding that you should highly take advantage of!