Eat less, ride more.

In your case, however, if you cut back on the junk food, I bet you would see some changes without necessarily restricting calories. At your height and weight, I wouldn't want to lose any weight at all. Rather, like you said, you need to add some muscle and lose some fat. I'd suggest doing some gym work for the upper body. Extra tone will probably help some.

Ultimately, though, losing fat means eating less calories than you burn off. But cut the junk food, if you can, and see what happens. I'm only a year removed from being an undergrad, so I know it can be a challenge.