Maybe someone with a Maggie will be by soon with something better. In the meantime...
Didn't find an illustration, but here are the manual's instructions for the '07 300. Probably very similar if not exactly the same in yours.
A/C Air Filter — If Equipped
The filter is located in the fresh air inlet under the hood,
behind a removable panel in the cowl on the passenger
side of the vehicle, next to the windshield wipers. When
installing a new filter, ensure its proper orientation. To
replace the filter remove the access door in the cowl
screen by pressing the retaining clips. Slide the lid on the
filter adapter forward and down and remove used filter.
Install new filter with arrows pointing in the direction of
airflow, which is toward the rear of the vehicle (text and
arrows on the filter indicate this).
When you open up the hood, its the grated plastic piece to the furthest back left you can get without hitting your windshield. Just press the two plastic tabs that are facing your windshield and pull up. Then pull out your air filter and put a new one in facing the right way.