How do you replace the day running light bulb?

I don't, but your owners manual does. if you don't have one you can download one FREE here: http://www.autousermanual.com/view/chevrolet/silverado/

The owner's manual explains this pretty well. You first have to remove the headlight. Only tip I can offer is to be VERY careful when twisting and pulling the sockets from the assemblies and the bulbs from the sockets. All the plastic is cheap, cheap, cheap. Also, buy long life (LL) designated bulbs.

Open hood, on the top of the headlight are two pins that you remove to take the headlight out so it can move out of your way, don't neet to take the bulbs out of it, then below where the headlight was is the parking lamps which has a tap that you push to one side and the whole light comes out so you can get to the daytime driving lights, the most inboard light on the lense. You can now remove this and replace the bulb, being careful to not touch th bulb itself and even then it is a good idea to clean it with alcohol to take off the oil left from your hands as it will cause the bulb to blow out prematurely.