I decided to give it all up and to change my life... (here, the decision was to do two things: to give up and to change)
I decided to give it all up, and I changed my life... (here, the person actually went ahead and changed their life as a result of making a decision to give it all up).
With the first sentence, you don't actually know if the speaker did in fact go ahead with their plan after making the decision.
With the second, it's clear that the speaker did change their life.
Student or Learner