Betty's journey from fluffy to fit...

You really need to help her lose some weight because her health will suffer if you don't. I agree with Keylarakat that first you need to take her to your vet and follow the vets advice for feeding. Exercise will help - you should have daily play sessions to actively engage her in physical activity. "Cat fishing" toys as I call them - something dangling on a string that she can jump at will get her moving. Maybe she likes to chase "jingly" balls - roll them on the floor and she if she will chase them. Try different things and see what she likes. As her owner you really need to get her in better shape - it will improve her health and energy and she'll be more fun to have around!