Before you read anything else stop and ask yourself the question:
"What do I need so I can be happier?"
Think about it carefully, and write your answer down.
Now you can go on.
Most of the psychologists doing this research claim there is nothing we can do about the 50% and 10%, but that we have total control over the 40%. I disagree. Although it takes a lot of effort, we also have some control over how we react to our circumstances and we can eventually change our set-point. The way that is done is by consistently making choices that make us happy. For example, instead of waking daily and fretting (vexing) over the fact that our house is too small and we need a house in a more affluent neighborhood, we wake each morning grateful to have a house and looking for ways to serve the people around us.
Now look at what you wrote down and decide where it fits in this discussion and determine what you need to really do to be happier.
Yes, it takes mental exertion and work to change attitudes, but it can make all the difference in the world whether we are happy or not. No one can make you happy. Happiness is a choice and only you have the power to choose it.