[zabatron]

First step you need to do is to clearly establish exactly what model Fiesta you actually have as pollen filter location varies between different models.If your car is a 2011 model then it is probably a WT Fiesta,not a WP which is the 2003-2005 model.
If your car is a 2011 WT Fiesta,then the pollen filter is located behind the lower centre cosole trim panel in the drivers side footwell.The access cover for the filter is is roughly a rectangular shape with one T15 Torx screw at the bottom of it.
On the Wp(and Wq)models,the pollen filter is located behind the lower centre console trim panel in the PASSENGER SIDE footwell.The access cover for the filter is also a rectangular shape but is retained by 4 torx screws.Note it is easier to access the filter if the glovebox is removed first by simply opening the glovebox and pressing in the sides of the inner glovebox and lifting it out.
When fitting new filter ensure arrow on filter is pointing to rear of car.