This is just a start up technique for most people (some use it for screaming though). Whats really important is that you just scream as you do now, meaning that sound, but apply the good technique habits little by little. When you breathe, your stomach comes out, your floating ribs at the bottom come out, and you lock down like your using the rest room. This all habits in no more than a second; if you draw it out too long your just building up too much unnecessary air. Thats what you really want to focus on first; get that breathing and support coordination down. Then try the scream again. Pay attention to where you feel it. Does it feel like your uncomfortably pushing your throat? If so, do it again with the attention on making it feel like it coming out of your mouth. When you can get it to that level, you can start playing with the tone to make it feel like its coming from the palate (whether it is or not is a style issue), sinuses, or back of the head. The sound isnt really coming from the places, but the resonance is causing the vibrations,and when you feel the resonance you know your doing it right. Its just a slow process really of experimenting. Unless im working with someone in person or through internet lessons with files/video being sent, its really hard to explain but you'll get it if you use enough focus.