Water pipes have started to humm when using the shower or at the end of toilet water tank fill. I understand it is the water pressure valve that needs to be replaced. I am looking for a step by step on how to replace the valve. TKS

Humming plumming! If I could set that to music with a rock-a-billy beat I could make millions.
By "water pressure valve " are you referring to the ballcock in the tank? I can tell you how to replace it but why not try this first. Shut the water off under the tank and open the lid. Now unscrew the three screws on top of the ballcock and lift and out the float ball, rod and stem assembly. Turn the washer over and make sure it's seated in properly. Now place a can overv the open valve and turn the water on for a moment to flush out the supplies. Reassemble and follow the tank adjustments that follows.
Check the tank water level, it should be at the mark in the tank or 3/8 to 1/2" below the top of the over flow tube. Now look at the flapper, If it has wavey edges on the flat surface, replace it. The linkage between the flapper and the flush lever should have 1/4" play when the tank is filled. Also, check the small tube coming out of the top of the bakkcock and make sure it's connect to and draining into the white overflow tube.. More questions? I'm as close as a click. TOM