Rid your pump of contaminants and debris. You'll want to turn on the water after removing the wand from the spray gun. Then squeeze the engine and hold the trigger. Do this until it produces a steady stream of water. You'll want to hold this for 2 minutes. Then push the safety latch and secure the spray gun's wand.
To change the oil of your pump, and this goes along with changing the oil from anything - you want to make sure it's turned off and cooled so you don't burn yourself. You should put on gloves to do this as to not stain your hands. You should also wear appropriate clothing that you would not mind getting dirty.
You'll need to remove the cap to the oil with a wrench. Once the cap is removed, drain the used oil by tilting the pressure washer. Once the oil has been drained, you can return it to its upright position and prepare to insert new, fresh oil.
Once you remove the pump's remaining oil, you'll want to fill the pump with fresh oil that is specified by the owners' manual. Your owner's manual should specify one to several different types of oil. Use a funnel to pour the oil in and not make a mess.
Make sure you pour in the recommended amount - no more, no less. You can do this by pre-measuring the oil or you can purchase pre-measured amounts. Only pour in the specified amount of oil necessary. Your owner's manual will tell you how much to use.
Make sure that after you put in the oil that you secure the cap tightly to ensure there are no leaks. Make sure you clean up any oil messes after.
You'll want to change your pressure washer's oil after the initial 50 hours, and then every three to five months, or after 500 hours. Your owner's manual to your pressure washer may specify an exact amount of time to change your oil and you'll want to follow those directions if they differ from these directions.
As always, if you have any questions about maintenance of your pressure washer pump, contact the manufacturer or a licensed retail and maintenance technician in your area.