Smile [Q] Hexa icons

Hello guys,

Monday i received mine Oneplus One and it is a true flagship killer. But i am not happy with the default icon pack, Don't get me wrong. I love it but, just a few apps get changed.

Now i am a designer and i would love to change the icons. But how can i change the .png of the app in the app drawer?

I have googl'd enough but i don't understand that, it is like abracadabra to me. Does someone have a really useful tut for me?

I don't want to create a new icon pack, i just want to expand the default one.