How to lose fat in an already muscular body?

So here's the story: I'm 5'4'', and about 135 pounds. I have muscular legs, but they still have fat on them. I did gymnastics and ran a lot for about 10 years, so those kind of added to that. My rib cage is also big, but I look wider in the middle because of it. I need to slim down in between my rib cage and my hips. My arms are also flabby, but I have a really hard time sliming them down. Running just doesn't help. I want to try the eliptical, but I'm nervous nothing is going to work! HELP!