If you reduce the number of calories you take in, you will see an effect over time - never instantly. Rember (it's probably not true, but is everyone's experience) that the weight you put on goes straight to your waist/bum/hips but when it comes off it does so evenly, from your fingers and toes as well as the aforementioned areas.
So yes, you should see a difference - but if you have replaced the alcohol calories with the odd chocolate bar or piece of cake, or even a cheese sandwich, then you won't see any difference, because there's been no change in the toal calorie intake.
If you want to reduce belly fat then you will have to do exercises as well as keeping an eye on the intake. The best way to tone-up/lose weight is to reduce calorie intake and exercise. If you don't currently take any exercise then you may want to check it is safe to do so with your GP; when you start, start gently - 20 minutes walking three times a week.
Look at the NHS direct website - I seem to remember that it had some good, basic advice on increasing levels of exercise.
But whatever you do, enjoy it.