Is it easy to replace the headlight on a 06 silverado? I am hoping it is pretty simple.

Can you get a replacement bulb from advance or somewhere?

Pull 2 clips out from the light on top and the whole assembly comes out. Prety simple.

can you change just the bulb or the whole assmembly?

You'll simply be changing the capsule. The reflector and lense assy stay.

Open your hood, and observe above the headlamp assy in question, TWO black metal rods pointing toward each other. With your finger, rotate each rod forward, so they are pointing to the front of the truck. Now, pull each rod up and out. Now you can tilt the lamp forward and out, to observe the lamp capsules.