DIAGNOSIS The washable air filter is behind the front lower grille, which is designed to snap off. It's not immediately obvious, so many folks miss it.
FIX 1) Make sure the unit is off. 2) Look at the lower front panel, just above the bucket. You'll see a slight seam. 3) Place your fingers in the recessed areas on the sides of this panel and pull firmly straight towards you. It's held by plastic clips and will pop off. 4) The gray foam filter is right there. Lift it out. 5) Rinse it thoroughly under lukewarm tap water until the water runs clear. Don't use soap or scrub it harshly. 6) Let it air dry COMPLETELY—this might take 24 hours. Don't put it back in damp. 7) Once dry, slide it back into the guides and snap the front panel back into place until all clips engage.
IF THAT DIDN'T WORK If the front panel feels like it won't budge, don't force it. Check if there's a small screw at the very bottom center. Some versions have one. If so, remove that screw first, then try pulling the panel.
HEADS UP A clogged filter is the #1 cause of poor performance, freezing up, and the unit overworking itself. You should be cleaning this filter at least once a month during heavy use. Mark your calendar.