You only need to change your behaviour to the extent that you want to change your lifestyle.
If you want to live a generally healthier lifestyle, you probably need to make small (but impactful) changes like adding some extra servings of fruit and vegetables to your meals, drinking more water, improving your sleep quality, increasing your general movement, and/or training 2-4 times a week. (But you don’t have to do all of them all at once. Focus on tiny doable things that you can consistently do.)
If you want to become a high level athlete then you will require a significant lifestyle change, which would necessitate significant behaviour change if you’re not already engaging in those behaviours.
However, so often people are told that in order to improve their health and fitness to suit the lifestyle they want, they need to embark on massive behaviour change and go to extremes. The demand of the changes versus the goal are often too much and people give up on it.
Wanting to improve your general health and fitness doesn’t require massive sacrifices or restrictions. It doesn’t have to take over your life or mean training instead of socialising, giving up other hobbies, or meticulously tracking your food intake.
That sort of behaviour change, for most people who just want to get a bit more active and eat a bit healthier, is not sustainable long-term.
Making smaller, manageable changes will still get you there and it’ll be more sustainable and more enjoyable along the way.