Working on it. Constantly monitoring yourself for negative self talk and turning that around at least in your mind as soon as you become aware of it. In time, the positive will become more normal for you than the negative.
A lot of hard work and an antidepressant
You have to change your perceptive of the past events that lead you to have a negative outlook. That does not mean you need to see them as positive. But reevaluate your reaction to them. I used to be really jaded myself, distrustful. It's neer a good idea to be totally trusting but you have to change your outlook.
Just one step forward