To change your unwanted behavior you need to replace it with something. You may need to do something to prevent yourself from sticking with your old habits. For example you can move the chair or couch you usually sit on.
If you want to get rid of a thought you need to focus on something else. When I meditate if an unwanted thought pops up I do not tell myself not to think about it. Instead of focus on the thoughts I want to think about. You could also try using visualization and affirmations