I have a faucet with a leaky stem, but I can't figure out what brand it is. (Picture attached.) How do I change the cartridge? While removing the ceramic lever is simple, accessing the cartridge looks like may need removal from below.

Are you quite sure it has cartridges and not washers?

have a faucet with a leaky stem
REmove the handle and chrome cover plate. You will find a nut on the stem. This is the bonnet packing nut.
Turn the stem until it begains to leak. Now, snug up the nut until the leak stops, Careful!! not too tight or the stem will be too tight to turn. Did that stop the leak? Regards, Tom