We have the power to make the decision to change but we do not possess the ability on our own to make that change.

Genesis 4: 7 (NIV)
7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it." 

In Genesis 4:7 I believe that God is saying to me, you must master your sin by calling on Me and I will deliver you. I am knocking at your door but you must make the choice to let Me in. The ability to open the door is on your side.