If you genuinely cannot exercise then I sympathise because that is going to make losing weight a lot harder for you (providing that you would have had the motivation to exercise hard, of course). Still, the same rules will apply - your calories in have to be less than your calories out, but nothing extreme. Over time, you will notice a difference.
There is a pretty simply rule that can be applied to avoiding dubious carb sources - if it is sweet, lose it, or at least minimise it (expecially with cereals, 'weight loss shakes' - rubbish anyway, and chocolate). Also, try swapping all of your current cereals to wholegrain, so brown bread, rice and pasta instead of white. Of course, the most ideal way to get your carbs is entirely through a source such as green vegetables and beans, but this isn't practical for most people - I certainly don't do this, but I'm not a ripped adonis either.