If you want to lose weight you have put your body in a position that it uses more calories than it consumes. There are two sides to the equation:

1) Energy Usage - Depends on your level of activity, gender, age, muscle mass, etc

2) Energy Intake - This is obviously controlled solely by your diet

So you can either increase your level of activity (cardio) or reduce your calorie intake (diet).

You can also increase your muscle mass but in order to do so your energy intake must be greater than your energy consumption. So you can see that having extra muscle mass helps to burn fat but putting on that muscle almost always comes with a little bit of gained fat.

I will assume that losing the fat is your main priority. To do I would suggest building a meal plan so you can keep your calories each day consistent. Follow your meal plan for a week or 2 and if you haven't lost weight then either increase the cardio level or decrease the daily calories slightly.

If you want to ensure the weight you are losing is fat and not muscle mass then you must put a little thought into your meal plan. Your lean protein should be nice and high. 1g of protein per pound of bodyweight is a good place to start. Your carb sources should be from complex carbs such as whole wheat pasta, brown rice, etc. Your fat sources should be from almonds, peanut butter, olive oil, fish oil, etc.

What type of exercises do you do at the gym? I would also suggest moving towards compound exercises with relatively high intensity. The compound movements will force your body to have to repair itself which in and of itself requires a good deal of energy to do so.

Hope this helps,

IW