Open up your UI in the UIBuilder. Select the MainHud tab across the top. Then, on the left hand side, expand MainHud and select the player window. Inside the player window, look for the icons. When you have the icon highlighted, go into the properties box in the lower left corner of the screen. Find the Size property and change it to your liking. You may have to change the minimum size as weill.
One other thing, changing the icon sizes will require you to reposition the icons.
Hope that helped.
