03redaccord

ok so my fathers honda just recently got couple of codes and the MIL light. the car is a 03 accord ex a/t with like 57xxx miles. we went to autozone and had it scanned pulled codes p0457(Evaporative Emission {EVAP} system leaked detected fue fill cap loose/offl) and p0420(catalyst system efficiancy below threshold). i checked the gas cap and it looked alright and i tightned it again. the p0420 i read that i need to update my ecm/pcm where would i do that. but what else needs to be done can someone help me out. oh and no mods done on the car stock regular oil changes