Changing the Air Filter on a 4th Generation Ford Mustang is incredibly easy, only one 8mm screw and two snaps hold it in.
The air filter needs to be changed at different intervals depending on where you operate the vehicle.
If you are driving your mustang around the southwest and dustier parts of the country,. You will probably want to change the filter twice a year or more.
If you are driving typical mileage in the southeast, once a year is probably fine.