First try changing the interior cabin microfilter. This is a $22-$26 part that you can get from your local dealership or online from retailers such as www.bavauto
. com and www.pelicanparts
Otherwise, the blower fan may need replacement. I suggest that you first pull out the microfilter to see if it is clogged.
Since you just bought the car, I recommend that you replace all filters and check all fluids. Many people get excited and forget about the basics.