Hmm… Bit of a can of worms here.
As a former chunky person, 5’9 and over 17 stone, I can relate to where you are.
Now as a 12 stone, 45min 10k runner, my top tips are:
– diet. Eat until you’re full, not till you feel ill, don’t eat crap, have some wine and cake occasionally. Almonds are a decent snack food. A packet of crisps now makes me feel I’ll. I eat a few crisps occasionally though.
– exercise. You’ll get faster with a combination of long, slow runs and faster, shorter sessions (especially intervals). Don’t run injured. Cycling is natural interval training (hills)
– core work/yoga etc is incredibly beneficial. You’ll be running more freely if that makes sense