How to change negative thoughts into positive ones

1. Understand that negative thoughts are normal - they are part of the normal human experience, they are not signs of a faulty mind. They are just products of the wiring of your mind to keep you safe.
2. Accept it as part of the normal human experience - understanding if not enough, you need to accept the thoughts even though it's uncomfortable.
3. Notice them - start to be more mindful and pay attention to when these negative thoughts comes up in you. Notice them as they do. Get good at doing this.
4. Deliberately change them - pick the thought bothering and throw it away, then replace it with a positive thought. With practice, doing this becomes automatic.