It's not as easy as it sounds, but it depends on how low your GPA is. After 120+ credits your average is generally pretty permanent. I finished my BA with a 3.5 and then got a MS with a 4.0. But each A I got toward my MS only raised my GPA by .01. Therefore, it took 10 classes to raise it by only one decimal point. If your GPA is a two-point something, an A would have a bigger impact, but you'd have to work hard and get all As. And if the end of your transcript was full of classes like Underwater Basketweaving 101, the board would probably see right through that, so just taking a bunch of really easy classes probably won't help you that much.
If your transcript is lackluster a good move whether you go Navy or not is to get a masters. In the amount of time it might take you to get accepted to OCS or find a civilian job you might just make it all the way through a masters like I did. I had to submit 3 applications before one actually made it to the board without being lost. And finding a job took me about 7 months (with the masters in hand).