replacing o2 sensors

I got a "check engine" light today, stayed on for about three seconds and turned off. I checked the codes and got a 32 and a 37 (both oxygen sensors). A few months ago my light came on one time, so that must have been for the other o2 sensor I guess. Anyway, should I just clear the codes and see if it comes up again, or replace them now? Is it something that needs replacing?