1. Turn off the vehicle and take out the key from the ignition.
2. Open the hood and find the cowls over the filter housing. You may need a Philips screwdriver to remove any bolts or screws that attach them.
3. Remove the cowls to access the filter housing.
4. Locate the locking tabs at the ends of the filter housing and disengage them.
5. Pull out the filter holding bracket and take out the old filter.
6. Inspect the filter for dirt and debris, and replace it if necessary.
7. Reinstall the filter holding bracket, close the filter housing, and secure the cowls.
8. Close the hood and you're done.
Note: The exact location and process of removing the cabin filter might differ slightly based on the model year of the Mercedes GLK you own. Consult your vehicle's owner manual for specific instructions for your car.