(No longer needed as of update 0.6)
To be able to edit the User Interface, it's first needed to enable the 'Advanced Mode', which will reveal all the hidden and advanced functions.
To do so, go to Options / User Interface. You will see the 'Enable Advanced Functions' button right under the unit system.
Tick the box to enable it.
Editing the User Interface
To open the User Interface Editor, press ESC and look for the 'Apps' button as shown in the image.
When you press the button, you will enter in the UI Edit mode. You have two buttons in the middle. The first one is to exit the UI Edit mode. The second one is to open the App list.
Here you can find all the avalaible apps. To choose one, simply click on it.
You can move the apps around by placing your mouse over the 4 arrows icon and dragging the app where you want. You can remove an app by clicking the X located in the top-right corner of each app. You can resize an app by clicking the arrow in the bottom-right corner of each app and dragging your mouse.
If you ever want to go back to the way the apps were before you edited them, press the red reset button (added in 0.6).