It's rare that I do a complete 180 with regards to my beliefs but it has happened (I was once a Christian. Later, I was basically what you'd call a New Atheist). What I tend to do is refine my beliefs as I learn new things. Incorporate the useful bits and trim away the obsolete bits. For example, I used to identify with the Left Hand Path as I admired the focus on individual responsibility and improvement. I still believe in that, but find that many of the surrounding principles are no longer useful to me.
Rather than ask for a definition of spiritual advancement, I'll give my rough interpretation of it. I would view it as the way in which a person comes to better understand themselves, the world and how they fit (or don't fit) into it. As such, it would do me no good to hold onto beliefs, or elements of a belief, that I no longer find fit for purpose.