Use the ideal body weight to calculate how much you should weigh.  Then you need to find out how many calories you need to obtain that weight.  To start slowly first find out how many calories to maintain your present weight, then reduce that by 500 calories.

If you are already eating healthy and working out you may just need to cut calories.  Sometimes it can be done by changing a few things you are presently eating.  You can easily do this by eating light version of anything you aren't doing now.  For instance,  double fiber breads & english muffins, go down one level on your milk.  If you drink whole milk got to 2% etc. Hope this helps.