Quit sugar. Seriously. After I restricted my sugar consumption, I lost 6 kilos without doing anything. World Health Organisation currently suggests that you consume 49g sugar per day which amounts to 7 tsp of sugar. We aren't talking about natural sugars in fruit or something similar but all sorts of added sugar in stuff like ice cream or sugar in beverages count.
For instance, a Magnum (ice-cream) contains 24g of sugar which is about 3.5 tsp. In a beer (alcoholic or non-alcoholic) it can be up to 3 tsp (21g). Some sorts like Radler can have more. Now calculate for yourself: if you drink as much as 2 beers it's nearly your daily allowance of sugar that you've consumed. You get my point?
Another thing to avoid as much as possible is all commercial baked stuff like cake, cookies etc and white bread. Unfortunately, if you often go visiting or receive visitors at home you can't completely avoid eating it as people's feelings get hurt when you refuse a piece of cake or a cookie. You don't need to be too puritanical about it, just don't eat too much (and remember, there is added sugar, too).
A solution could be to bake more at home using other types of flour than white and less sugar. In nearly every recipe, you can cut on sugar and it still will taste fine.
So if you just follow these two simple rules, you'll go a long distance in losing that extra weight without going on a diet or killing yourself with exercise. Unless you are so poor that sugar and white bread is all you can afford instead of meat, eggs and dairy. In this case you'll probably stay thin anyway because of undernourishment which luckily seldom happens in the West nowadays.
P.S. Some people have to eat white bread because of health problems. In this situation, you can low its GI by a) freezing it; b) toasting it; c) doing both.