basically calorie deficit.

it's the most natural way to burn excess fat in your body. also strength training helps to convert fats into muscle. watching your diet is also essential.

walking alone is insufficient to burn your daily calorie intake - unless you really measure to the dot and you are confident that your walking is burning > intake.

conditioning workout works too. combine a couple of exercise together to make it more effective.

high protein diet, less carbs / oil / fats / trans fat / processed food is essential to this build up. also perhaps can consider some probiotics for the stomach and gut health.

it is a long process but just never give up on the motivation - keep yourself disciplined and you will reap the rewards eventually.