Drop the gas tank and take the old one out and put a new one in.
the fuel pump is in the gas tank
You replace it when it fails.
I have a 1996 K1500 and you do not need to replace the whole sending unit unless your fuel guage is not working properly. Just make sure that you replace the fuel pick up screen when you replace the pump, do not reuse the old screen as it may reduce your new pumps ability to pick up fuel resulting in low fuel pressures. I have a 1997 K1500 and have replaced only the pump a couple times. It is much less costly than replacing the entire tank level sensor etc..
The fuel pump is in the tank and the tank must be removed to replace it.
location of fuel pump relay
the fuel pump is in the gas tank the tank must be removed to replace the pump
In the fuel tank
You can't by just looking at it. Just replace it.
you need to drop tank fuel pump is in tank
Yes.
Inside the fuel tank
You must remove the fuel tank as it is located on top and inside the tank, unless you can remove it without dropping the tank.