Yep - diet or exercise or both - do whatever works for you. Take 3500 calories out of the equation by whatever method you like (more or less), and you'll lose a pound. It's just not going to come off your tummy, no matter how many crunches you do. Sorry.
If you include exercise you'll probably be healthier.
It's pretty straightforward. It's not rocket science.
And yeah, a lower percentage of body fat is more important than hitting the "right" weight range in the charts.