Oh...well I think you just download it, then on Edit Settings (from the menu in the top left) you choose Identity and then Change Avatar button. That will allow you to choose the new icon you downloaded from your PC.
Hm, I practice a lot! I find pictures of foods, and then draw them on my computer! But then I take much time shading it and making it look right...perhaps you can use a tutorial? I'm not much good at teaching..