squeaking fan

Pulled up last night and since the engine was warm the fan(s?) stayed on for the customery minute or so. With the engine off I noticed a squeaking from the front of the car which I'm guessing was one of the fans (I think it has two, maybe I'm wrong).

Might be nothing to worry about but, in the event that I need to replace it, how difficult a job is it to get the old fan out and the new one in?

Cheers,

iep