It's actually pretty easy.
Click twice on your character on the layout to open the sprite editor, then you'll see the colors on the side. Notice the top big box that probably has either white or black in it. If you right click it you'll see set transparent as one of the choices. Select it then use the fill tool to fill all your white background with the transparency! It's much easier and you can use it while using Construct 2. :) Hope this helps.