To replace a cartridge for a Spring Faucet, locate the small, round set screw cover on the handle.
With great care not to damage the finish, pop the cover off by getting underneath it with something thin.
Once the cover is off, use an allen wrench to remove the set screw inside.
Pull the handle straight out to remove the handle and expose the top of the cartridge.
Using only your hand (no tools) unscrew the bonnet around the cartridge.
Using a wrench, unscrew the exposed brass nut.
Now the cartridge will pull straight out.
Repeat the process in opposite steps to install the new cartridge.