Your options are:
- visit the town of Narita (one stop by local train, bus, or taxi). It is a sleepy country town with a few temples, but otherwise not much to do.
- get a day room at one of the many Narita hotels
- take the 'Limousine bus' downtown, but it may run into traffic jams at rush hour on the way back, which is especially not desirable in your case
- take the Keisei Skyliner train (1 hour) to Ueno and walk around for 2-3 hours. Ueno is a bargain shopping and office area, with (among other things) a park (with beautiful cherry blossoms coming soon), a zoo, and many eateries. Some of the Ueno-Narita evening Skyliners stop along the way to unload commuters, and therefore take over an hour.
- take the Narita Express train (1 hour) to Tokyo station, walk around for 2-3 hours (upscale Ginza and the Imperial Palace grounds are nearby).

Given the limited time at your disposal, I would go downstairs to the train departure area and take the first outbound airport train, Narita Express or Skyliner, both of which run once an hour. Do NOT take any of the other trains running on the same lines, they are local trains which will take over 1:30 hours to reach Tokyo. Ditto on the way back, as it will be rush hour and commuters will pack into those local trains.