Diet is the best means by which to lose weight. Exercise is a good addition to help you tone up as you lose the weight.
It's pretty simple to lose weight for most people, you just need a calorie deficit. Look up your recommended calorie intake per day, then work out a meal plan which comes in under that daily calorie amount. So, for example, if your daily calorie recommendation is 2,000 calories then work out daily meals to add up to say 1,700 calories per day. Of course, you need to factor in any health issues and your daily activities. If you did a manual job you might need more calories, but that should be factored into your daily calorie recommendation anyway.
Cutting calories usually means cutting out sugar for a start. That's step 1. Foods to factor in can be those such as plain white rice, grilled or boiled chicken, plain breakfast cereals with low fat milk or even non dairy milk substitutes, fresh vegetables, salad, etc. Be careful with fruit because that can contain sugar. Smoothies using things like greek yogurt, banana, strawberries, etc, can be a good meal substitute. You can sweeten with a sugar substitute like stevia.
Basically just get a calorie deficit going and cut out excess sugar as your main two goals.
