Runs but doesn't seem to be cleaning the air,...

Question

Hello! We bought this unit from someone, however it was new. It ran great, and still does but we don't smell that smell we once did and so my husband seems to think we need a new filter. I thought I had read somehwere that the filters in these things don't need to be changed but once in a great while, but I could be mistaken. Does it sound like the filter is indeed the problem?