It's all about balancing your nutrition input Vs. burn rate of said nutrition. The guys I know that have had the most amazing bodies all have very strict diets.
Try eating smaller portions 5 times a day and makes sure it's low fat, high protein and some fiber. This keeps your engine running all day slowly feeding your recycling center makes it run smoother than just throwing down two huge meals a day like most people.
Next you have to hydrate properly with either straight water of a good sugar free electrolyte mix. I try to drink 3 liters a day, 4 if I am playing singles in the heat.
A brisk 15-20 minute workout every day on top of tennis 3 times a week should be sufficient to lose weight as long as you are serious about what you eat.
I like to use my hydraulic stepper in the morning for 5 or 10 minutes to warm up. This keeps the burn going in my legs all day long!
This is the one I have, and it blows your legs up! If you can do this bad boy for 10 minutes a day and throw in 5 minutes of push ups, you will see and feel a difference in your fitness level very soon.