Changing a person.
Helping a person change.
There’s a difference between those two; an important distinction. The former is having an idea for how someone should be and convincing them to change. The later is supporting their own decision to change. Both can result in positive outcomes. One requires a degree of egoism in your own ideas and a pressure on a friend/lover that can easily turn toxic. Changing a person is claiming to know who they should be better than they themselves know. You cannot know this; you cannot exert your will upon them without disregarding their own will.
The strongest bond you can form, the ultimate goal of love, requires total acceptance of another person. When you do this, you can’t try to change them, for that would be denying a part of them.. Even if it’s a minute part, some flaw you think is unimportant, it’s one brick in the castle. Every brick has it’s place.
Blind acceptance is equally negative in the long term. Loving them in this one moment, loving just exactly who they are now, it will fail. Stagnancy is no way to live a life, it must be fluid and growing. Growth requires change. So you must accept who they are in totality and then support their initiatives to change. Foster their goals and help them to become the person they wish to be.
Not the one you think they should be.