T.H.
What have you tried? I would try washing it. You can add a little bleach or Oxy Clean to the wash and that helps a lot. I've moved away from bleach mostly, but I do use it in a pinch or if something is really dirty. You don't need a lot and if you use a little bit it won't fade the other colors on the jacket, if there are any. If it's a fleece I would try soaking it in the sink with water and Oxo Clean first, then washing it with more Oxy Clean.