Just to add some comment on this. Its not about pushing the thoughts away. As said its about accepting the thought as they are coming and let them go away. So idea would be to recognize it as a negative thought and let it go and add it with new positive thought. So its like building a neurological network(not sure if it is termed that way) were you train your brain to recognize the negative thought and let it go without giving much importance, that is not letting your brain to create deep emotion out of it and also making sure it is accompanied by new positive thought to impact positively to your emotions.

Hopefully I am right as its what i thought and would be of some help.

Regards, Aru