You're on the right track with disassembly for replacing the steering stop, but there are a few things to consider to avoid damaging the components. The top
ball bearings race is likely a press-fit onto the steering column. Gently tapping with a mallet might not be enough. You'll need a steering stem puller (also known as a triple tree puller) to remove it safely. This tool threads onto the top of the steering column and applies pulling force to separate the race from the stem. The circlip holding the bottom
roller bearing is likely located at the bottom of the steering stem, inside the frame's head tube. You might need a good flashlight to see it. It might be a snap ring style circlip requiring specialized snap ring pliers for removal.