Diagnosis
The filters are held by two spring-loaded latches. They require a specific angle and pressure to release.
How to Fix It
Open the microwave door. Place one hand under the filter for support. Push the filter UP slightly, then pull it DOWN and TOWARD you. It should pivot down about 30 degrees before you can pull it out.
If That Didn't Work
Grease buildup can cement the filter in place. Use a degreaser around the edges and let it soak for 10 minutes. Try the removal motion again.
Heads Up
The filters are aluminum. Do not use abrasive scrubbers. Wash in warm soapy water or dishwasher (top rack only). They must be completely dry before reinstallation.