2008 GMC Sierra Heater Core
 

Well I just bought a used 2008 GMC Sierra 4X4 P/U
And when I turn on the heat I smell antifreeze.
So I am guessing I need to change the heater core?
What do I need to do to make this happen?
Is it a all day affair or a couple of hours?

I am guessing I drain the coolent first.

Any help would be great.
Also if anyone can direct me to a repair manual that would be great too.

Brad