How Much Weight Can You Realistically Lose?

Losing weight is tricky because your goal is to lose fat and hang on to every ounce of muscle. I want to emphasize that your focus should be on losing fat and not necessarily weight.

The only way to lose fat is to burn more calories than you consume. If you are maintaining your weight now, then you are eating an equal amount of calories to what you are burning. To start losing weight you have to either cut calories from your diet or increase the calories you are burning from activity (or preferably, both.)
You have to be careful that you don't cut calories too much because you still want to maintain your energy level and your body's ability to recover. If you do cut your calories too much, your body will go into panic mode because it thinks you are starving it. Your metabolism will slow down to conserve precious body tissue and you will stop losing weight.

It is best to lose weight slowly, shooting for two pounds of fat per week. When calories are restricted, the body will prioritize energy provision over growth and repair. Protein needs increase during periods of caloric restriction.
You will need to "feed" your muscles with protein to keep your body from breaking down muscle tissue. While losing body fat, you should try to at least maintain if not gain muscle mass. Muscle burns calories that will make it easier to lose fat.

The more muscle you have, the better you will look and it will be easier to maintain your goal weight because your metabolism will be high. Losing a pound of fat per week may seem agonizingly slow, but it will be so much easier to keep off in the long run. At the same time, the scale may or may not change depending on how much muscle you gain.

Be sure to include resistance training as part of your weight-loss plan along with a balanced diet and proper cardiovascular exercise.