If you’re looking to change the composition of your body your goals must be defined. Not only that, but you have to be consistent with your nutrition
Slimming down and building muscle are two different fitness goals that require different nutrition objectives.
Your goal is to create a calorie deficit. The best way to do that is with a low-carb diet. This consists of lean protein and veggies in every meal.
Your goal is a calorie surplus. You need to eat more and combine that with a routine strength training program to see results.