Tip unscrews, push old filter out, put new filter in, screw back on.
Don't forget to wrap the tip you just removed with blue painters tape as that will help with reducing false hits. Electrical tape or duct tape is bad as it will set off meter.
Also, hold down the auto zero and it will turn of the auto zero. you will have a low tolerance to refrigerant concentration helping you find leak faster. Pushing the auto zero when of will rest to new level if in higher concentration.