I haven't COMPLETELY turned my life around, but every 5 years or so, I do make many major changes.
Five years ago today, I was married, just finishing my doctorate, and looking for a house. Since my wife was away most of the time with her boyfriend, I spent most of my time playing computer games. I was fairly antisocial and rarely went out - I was willing to go out, but got tired of explaining why I'm there without my wife. While I had been in sports in my youth, I was pretty much exercise free for years. I ate out most days and drank tons of soda. I hit a recent bodyweight low of 120 lbs.
Five years later, I'm divorced, found a new GF, and will be married again in 9 months. I play computer games, but I keep myself to usually 30 minutes or less a day and none of them are computer intensive - my computer is over 3.5 years old and wasn't even a great computer back then. I try to go out as much as I can, I invite friends over for dinner parties, etc, even though I am still quite shy about it. I've really gotten into remodelling and I'm getting the house ready to be sold. I've been lifting weights for the last 1.5 years and try to eat healthy (I rarely eat out and I don't buy soda any more). I've happily put on 30 pounds.
I've done similar things every 5 years in my life. I moved at age 5 from California to Nebraska, losing all my friends and starting school. At age 15, I changed my whole outlook on life, tried eating a wide range of foods instead of being picky, and started many school activities. At age 18, I dumped all my friends and activities and moved to college. Same thing happened at age 22 when I went to grad school.
Most of the changes were pretty easy. To stop an activity, just don't do it. To stop drinking soda, just don't buy it. Quick and painless. But things like divorcing my wife took nearly 3 years. The first half was denial. The next year was testing her (will she kiss me once or let me kiss her without her backing away once in the month of February - a month that contains both Valentines day and my birthday) and watching her continually fail the tests. Then it was a few months of slowly gaining the courage to divorce by having painful conversations with everyone I knew. The divorce itself was quick and painless. Actually it was more of a relief than anything. Starting to lift weights for exercise was easy, I just one day did it. Yes, I stopped at one point but I restarted and I've been doing it ever since.
Really the hardest of all is eating this horrible crap called mushrooms. They have little taste (ie they water down the intense dish flavors), and the little flavor they do have is of mold and dirt. Yuck. I still have a lot of difficulty putting those nasty mushy things in my mouth. Same goes with seafood, but they don't taste of dirt, they taste of rotting sea stench.