DIAGNOSIS You're right to be careful—the front grill on this model is a single piece that needs to be removed a specific way, not just pulled.
FIX Unplug the unit first. Look at the top corners of the front panel. You should see two notches or indentations. Press firmly inward on both sides of the panel at these notches while simultaneously pulling the *top* of the panel forward. The top should unclip. Once the top is free, lift the entire panel up and away to remove it. The rectangular foam filter is right behind it. Slide it out, wash it in lukewarm water with mild soap, rinse, and let it air dry completely before reinstalling.
IF THAT DIDN'T WORK If the clips feel completely stuck, don't force it. Sometimes the plastic warps slightly. Try pressing the notches more firmly and using a thin plastic pry tool (like a guitar pick) at the seam to help release the clip without cracking the housing.
HEADS UP Never run the unit without the filter. It'll coat the evaporator coil in dust incredibly fast, which kills cooling efficiency and can cause the E3 error code from poor heat exchange.