I started out at 5'9", 235 pounds. I have a desk job and I'm a couch potato by nature. I used to use the upperstairs bathroom to get extra exercise. After I started biking last May I got down to 195 and have kept it off through the winter.
Weight loos is all about calorie imbalance. If you burn more calories than you consume, you lose weight. Some people's bodies seem to burn calories better than others. One thing you can do about that is add muscle. Muscle burns more calories when you're sitting around watching TV than fat does -- really.
So I've been going to the gym regularly. I mostly do upper body and core work. I do leg curls because it helps with biking, but biking won't build those muscles. Same thing with core (abs, back, etc.).
I've also been trying to work in more flexibility/stretching stuff because it helps prevent injuries when you crash on the bike.