Yes, cardio will reduce the fat everywhere, including upper arms. So that's an excellent suggestion.

However, exercise with light weights--and the muscle tone you acquire--will also be very helpful. Don't worry about looking bulky. You're a female, right? You don't have the testosterone for bulk. When the fat is reduced, your arms will look shapelier, which is what you want.

I use Cory Everson's video workout Get Hard Arms with excellent results. I also like Gilad's Men of Steel Arms workout. There are countless excellent video workouts available, or you can get a book from the library or a bookstore on ways to workout those triceps, biceps, and shoulders.

Keep in mind that those "cut" arms you see on movie stars and fitness models are very unusual--a combination of very low bodyfat and very hard weight work. Not very likely for most of us.