You make a conscious decision to change it. As for making life easier? You will have to still face all of life's challenges, they just won't drag you down, and can make finding solutions easier.
I have a friend who was always complaining about life. A year ago someone gave her a book about gratitude and positive thinking. One of her biggest complaints was her job. Once she started looking at the positives, she realized it wasn't her job she hated. She actually loved what she did. It was her employer that was the problem. She starting looking around for another place to work. She found one. Not only is the boss better, but the co-workers are happier making for a much better work environment. AND she now makes more money and has better hours.
Focusing on what is good about your life makes it easier to fix what is wrong.
She started her change by starting her day listing 3-5 things was thankful for. She posted them on Facebook. Some friends liked it others complained. Those that complained are not getting much attention nowadays. Those that supported her are. Surrounding yourself with positive people helps. I really enjoyed her positive posts because it made me think about what I am grateful for.