Run the engine first to heat the oil. Doing so makes it run more freely.
Use a 9/16 wrench to remove the oil drain cap from the Jeep's sump. Be careful as the oil will be hot from running the engine. Do not get any used engine oil onto hands or skin. It is highly carcinogenic. Allow the oil to fully drip out, collecting it in a suitable oil pan or container.
Once all the oil has drained out, remove the oil filter. It is positioned right below the oil dip stick. When installing a new oil filter, put some new engine oil on and around the rubber seal. Replace oil drain cap.
Fill the engine back up with 6 U.S. quarts of SAE 10w30 motor oil. In colder climates, 5w30 may be used. Be careful not to overfill by checking the level on the dipstick. Once the correct level is reached, replace the oil filler cap and run the engine for about 30 seconds to let the oil circulate around the engine and into the new filter. Check the level now and top up if necessary.
API SL or ACEA A3 rated oil should be used. API SM and SN oil does not provide the wear protection required by the flat tappets in the AMC 242 engine.