If you're retracing a whole design:
- Go to the designer if you're not already there.
- Click on the button at the top left and choose Import Design. This assumes it's saved as a picture file: JPG, PNG, etc. Turning on the Fade option usually, makes it easier to distinguish new lines from old.
- Draw over each line.
- Select the eraser tool and double click on the original image (away from the lines you drew) to delete it.