Small changes in your diet aren't going to make you thin:

Numerous scientific studies show that small caloric changes have almost no long-term effect on weight. When we skip a cookie or exercise a little more, the body’s biological and behavioral adaptations kick in, significantly reducing the caloric benefits of our effort.

 This is why it's insane to worry about whether you eat dessert or not.  One cookie more or less per day isn't your problem.   

This is also why it is pointless to worry about your weight as a separate issue from your overall health.  Setting your goal as 'losing weight' only makes you into a miserable counter of infinite calories. 

The reason to make small changes in your habits is that they are practice in changing habits.  You don't change habits all at once; you change one until you do it automatically.  Then you do it again.

The thing about acquiring a healthier lifestyle over time is that it feels good over time.  You start to crave exercise and healthy food; you start to notice that junk food makes you feel blah.  Pretty soon it's more painful to go back to the old habits than it is to acquire new ones.