Start to notice how these pictures are constructed and what form they take.
Are they three dimensional or flat, colour or black and white? What is there size relative to life and are they focused or unfocused? Are they bright or dim and do they have motion or are they still?
A very simple method of dismissing a negative image, is to make the image much smaller and change it to black and white. Try to make the image about the size of a postage stamp and then simply push the image away from you and into the distance so it can no longer be seen and then start to paint a new picture.
Make the new picture as bright and colourful as possible and try to include as much detail as you are able. You can also add an uplifting soundtrack to your pictures as well to increase the effect.
Another way of re-framing an image, is to see the negative picture in your mind and then start to become aware of a spot in the middle of the image. Now start to imagine the spot growing and as it grows you notice that your new image is developing over the old image. Continue to observe your new image until it fill the canvas, completely covering the old one.
Of course, your new painting is much more vivid and beautiful than the one it has replaced.
Repeat this process several times until you are sure that you see this picture instead of the old one.