Help me to loose belly fat

Hi everyone. I am looking to get in shape. I look fit overall except for my belly fat which I have just let it go out of control. I am looking for any suggestions regarding diet, exercise etc. I am 30 year old, 5ft 6 inches, weighs 138 lbs. the only workout I currently do is walk for around 40 minutes at 3miles per hour on treadmill. Please help me out. I am very concerned that my health is gonna get bad if I do not lose some belly fat. I have never been pregnant but would want to be in my best health whenever I do. I cannot attach my pictures but it’s getting really bad and I have line in my belly from the folding in recent years.