The Serenity Prayer asks The Eternal for serenity to achieve acceptance, and then for courage and wisdom. Connecting with the Divine can bring serenity if one opens fully, allowing the feeling of peace to flood in. If one silently chants the prayer, or a portion of the prayer, "God grant me serenity" for example, for ten minutes a day, every day, and thinks nothing but these words during those daily ten minutes, one will probably notice after patient persistence in this practice that serenity will begin to come naturally. Any set of words that brings you a feeling of peace would accomplish the same effect, but appealing to the Higher Power in this way directly acknowledges that Power and invites God to take an active role. This cannot be a bad thing.
Once serenity is achieved, one tends to trust one's existence more. Feeling connected with the Almighty gives one a feeling of security and warmth, and when one feels secure in themselves acceptance comes naturally. You stop sweating the small stuff, but begin instead to truly enjoy it. Things that really annoyed you before just don't seem to matter as much.
Automatically, therefore, you find less that needs changing. But usually the things that truly need changing the most are found within. They are obstacles to serenity that we create for ourselves - fear of the future, regret of the past or failure to forgive ourselves. To change these things, as anything, requires courage. Personally I find courage in trying always to do right and in detachment from outcomes. Others find it in their trust of the Divine.
Wisdom comes from study and experience. Using your serenity to observe without judgment, you see life unfold much more clearly. All experience contains lessons for us. You may believe that God brings you experiences for the express purpose of teaching you wisdom. To believe so prepares you to be ready to learn always from life.
May all your days be serene.