Step one - stop eating junk food, ALL of it.
For this for 2 weeks, eat only this
bowl of porridge for breakfast
chicken salad for lunch
steak and grilled veg for dinner
one piece of fruit
No coke, no bread, no potatoes, no kebab, no biscuits with your tea, no crisps between meals, no snacking whatsoever (I MEAN IT!) The above is all you eat.
Feel free to substitue chicken with tinned tuna, steak with grilled chicken or salmon or even pork chops.
Don't eat anything process, anything that comes in a plastic bag. Drink only water. You won't die ! Prisoners in concentration camp would consider that a feast and they survived on a LOT less doing hard labour. You can live on that easy sitting at home playing video games.
Try it for 2 weeks, if you don't lose weight I'll go eat my hat.