How do you increase the 400 meter time?

Since the 400M is 5% Aerobic and 95% Anaerobic, you need to train mostly on your Anaerobic system. First I would do some short sprints(around 50M-100M) to build raw speed needed for the start and finish of a 400M race. When you have that down, go to your local track and run some intervals ranging between 100M-400M. Running intervals will teach your body to handle lactic acid at high speeds which is needed in a 400M race(This will prevent you from dying in the last 100M).Try not to run intervals more than 400m because then the extra distance will make you end up running slower than your racing speed, which will teach your body to run slower than goal pace (not a good idea). Since their is only a 5% Aerobic part in this race, it would be a good idea to run a longer distance once or twice a week. If I were you, I would not run over 2 miles because if you run farther than that, you are then replacing the needed fast twitch muscle fibers with more slow twitch muscle which is not what you want since this is a fast event. Remember, just train hard and DON'T SLACK OFF!!!!!.