After writing an answer to a similar question, "What's the most significant life-changing event in your life?" - I see your question more fits my story.
As I wrote there, small changes taken together become a process of change. I think especially if one is on a course of conscious self-evolution.
The small changes that have added up to significant shifts have stemmed mostly from a choice to let go of old fixed ideas, let go of attachments to how things have to be and also to material possessions.
At first it was definitely not easy to let go of things I was attached to, but after practicing this type of letting go for the past 13 years, it becomes easier and even joyful as I have found in letting go a true freedom. It is also becoming more natural to let go of hard-headed ideas of what is right and wrong, to humble myself and let go of reaction and defensiveness. The reward is living more of who I really am.
An all-at-once big change, a major turning point, came when after a traumatic event I reflected on what I believed and why. That story is also told more fully in the hub, "What do you believe and why?"
After writing out principles to live by, a few years later I chose to be true to myself, and that choice set me off on a real life adventure which has shown me that until then I was not truly alive.