The overall approach to changing your eating habits is to systematically eliminate unhealthy items and find nourishing and delicious replacements for them.
Switching over can be immediate or gradual. The most dramatic results are realized by adventurous folks who aren’t afraid to make these kind of big changes all at once. However, it is fine to make incremental changes at a moderate pace, or even rather slowly for those folks with a more timid disposition.
A gradual switch over might begin with a small selection of maybe 3 to 5 of the most egregious ingredients in your old diet. Once you’ve become comfortable with the new healthier substitutions, you may continue to phase out more of the most unhealthy ingredients a few at the time.