just do some cardio if you want to get leaner. I'd say rowing is my favorite cardio workout (besides swimming) because you're working your core while you're rowing, it feels good the next morning.
But really, any form of cardio will begin to wear away at fat. If you don't want to lose the size you'll have to deal with shrinking before you grow. At least that's what we're taught. Anyways, just do some ab workouts, crunches with weights and things like that.
Also, "core" workouts really help get the lines showing, so a plank, side-plank, or superman work well (normally together) and whatever else you can find. So like 30-40 seconds each and work up from their as you're muscles build their endurance.