Shut off the water valves under the sink to stop water flow to the faucet.
Remove the set screw on the handle with an Allen wrench. This is located on the front near the base of the handle. Slide off the handle once the screw is out.
Slide the cartridge cover off the base of the faucet. This comes right off once the handle is removed. Loosen the three screws securing the faucet to the base with an Allen wrench.
Remove the cartridge itself by pulling it up and off the base of the faucet. It may be necessary to remove the three O rings by hand as well if they remain in the faucet after the cartridge is removed.
Replace the O rings with new ones and then slide the new cartridge into place on the faucet. Tighten the three cartridge screws to secure it, and slide the cover over the cartridge. Press it into place over the base piece below the cartridge. If your cartridge uses an adapter on the stem, replace this after sliding the cartridge cover into place.
Slide the handle on the cartridge cover and tighten the set screw with an Allen wrench.