Firstly, we see Dorian's desire to change the course of his life after he is so cruel to Sibyl Vane after her lacklustre performance at the theatre. Being shocked by the slight change in the portrait that he can see, he determines to be better and to end his relationship with Lord Henry:
He would resist temptation. He would not see Lord Henry any more--would not, at any rate, listen to those subtle, poisonous theories that in Basil Hallward's garden had first stirred within him the passion for impossible things.
However, of course, he is defeated by the death of Sibyl, who, in anguish, committed suicide. After this, we move towards the end of the novel when Dorian tells Henry he has determined to "be good" and cites his refusal to seduce a country girl as evidence:
"Suddenly I determined to leave her as flowerlike as I had found her."
However, it is only when he sees that this action, which he hoped would change the portrait for the better, as blatant hypocrisy, that he realises his best intentions were thwarted. It is in the last chapter that he determines to destroy the portrait and be good:
Perhaps if his life bcame pure he would be able to expel every sign of evil passion from the face.
Of course, his determination to destroy the portrait ironically only ends in his own death, and the reversal of the magic, making his own body foul and restoring the portrait to its original beauty.