remove old brass tap
What are the next steps?


I don't know all of them but I suspect they start with


lift the handle off the splined shaft (it may be very stiff)
look for a locking nut that secures the valve mechanism into the body of the faucet


this may be hidden under a brass skirt that can be lifted when the handle is out of the way

lift out, or unscrew the valve mechanism
remove the washer from the bottom of the mechanism - it may be held in place by a screw.