Assuming you are talking about the raised white letters on your tires, and you want to remove the blue color that is on them, here are a few steps that should help you out. First, start by scrubbing the blue color with a tire brush and some soapy water. If this does not seem to be working, then you can try using a tire cleaner or even WD-40.
Just spray either of these onto the blue areas and let it sit for a few minutes before scrubbing again. If all else fails, then you may need to resort to sanding down the blue areas with sandpaper until they are gone. Just be careful not to sand too much and end up damaging the raised white letters themselves!