It's not possible for you to change your own heart, but it's possible for God to change you by the miracle working power of His Spirit! He'll do things you can't do!
This is what it means to be "born again a new creature in Christ Jesus.--Old things shall pass away and all things shall become new!" (Jn.3:3; 2Cor.5:17) His coming into your life not only renews and purifies and regenerates your own spirit, but it also renews your mind, literally breaking old connections and reflexes, and gradually rebuilding and rewiring it into a whole new computer system with a different outlook on life and a wonderful new way of looking at the World, with new reactions to nearly everything around you. (Eph.4:23; Rom.12:2)
But it's impossible for you to make such a change as this yourself. "For with Man it is impossible, but with God, all things are possible!" (Mat.19:26) If you want this change, it's necessary for you to ask Jesus to come into your heart. He's the One who makes "new creatures"! All you do is ask Him to come in, then He works the miracle!
Of course, some changes are instantaneous, others take awhile.--But if you're genuinely saved, you'll be changed, because He changes people!