How can I get my cat to lose weight?

my cat is about 8 years old, and I’m afraid she won’t live a long life unless she loses weight. I switched the way she eats from those self-feeders to a small bowl. I’d put a picture up of her on here, but I’m on my phone so can’t: basically, she’s so fat that when she runs, you can see her fat on the bottom of her stomach wiggle back and forth. Any other cat owners have (or had) the same problem? What can I do?