I choose... none of your choices.
Personality can be changed, but it's super difficult. You have to model and act out the behavior you want on a daily basis, with constant reinforcement of that behavior. Eventually it becomes a personality trait, which in turn stays with you until you change your personality again.
Type B people can go to Type A, lazy slobs can turn into self-disciplined nutty goal setters, super athletic folk can turn into potato chip eating, sit-in-front-of-the-TV-and-do-nothing average people. It depends on what behavior you want to instill, and if there's going to be reinforcement for that behavior. (Self-discipline can work, but it's a lot easier if you have the right context. Why would you work on a personality trait like self-discipline if you have nothing to become self-disciplined for?)
The younger you are, especially if you're in your early 20s or younger, the easier it is to mold your personality. It's not impossible if you're in your 30s, 40s, 50s, etc., it's just much harder.