I recently went to Advanced Auto Parks and these are the codes my car is showing. I bought a new O2 sensor for the P0420 code but I can't get the old one out. Also I am not sure what this other code means. Help?

 

When I had to replace mine it took awhile to get it out and when I was about to give up it finally lossened up. The other code P0740 is basically a code you don't want to see. It is a torque converter lockup malfunction. Usually when you get this code it's not to long before the tranny goes out, don't ask how I know try to reset the codes after you get the O2 sensor replaced, if the codes don't come back i wouldnt worry about it right this second but start saving a tranny fund. It took me 50-60k miles before my tranny failed from when I first got that code.