How can I gain the will power to pick healthier things to eat? I have trouble with that

You have to develop the desire, the need to make your body healthy, it is really easy, but it takes motivation, if you need some, go to your local hospital, and look in on people who are on life support, or lung machines, kidney machines, or are so obese that they are bed ridden, checkout the heart ward, or patients with weight related diseases... One trip to a hospital, or emergency ward might change you!

You might want to read these two blog articles: My Health Essentials: Reprogramming The Food Thought Process

My Health Essentials: Developing Discipline

Think also about the fact that you want to change and then write, mabe a small journal, on how you want to make small changes, to achieve your goal. Like today or tomorrow, I'll have a chicken salad, instead of a burger, or pizza. And then the next day, try some whole grain cereal, eggs, toast or yogurt, Maybe cut out soda and drink whole fruit juices or water. Fruits, nuts, seeds instead of chips, candy and cakes. Small changes are easier to accept and work into your life.

Another idea is to get rid of the junk foods you have now in the house and make a list of only healthy options to have at home then go food shopping. Easier to skip the cookies and such if they aren't tempting you from the kitchen... :)

Find healthy recipes for healthy foods you like.
Like instead of eating a bag of potato chips
Make some healthy potato recipes.
Find healthy dessert recipes for when you crave sweets.