Scrap the stain with a blade or scrapper. This will help in removing the top layer quicker. Perform this step only if the paint is dry, otherwise skip step 1 and 2 and directly start from step 3.
Now sprinkle a little water over the stain to make it a little damp. Make sure that you sprinkle a little water and try getting the paint off before adding more.
Once the stain gets damp, its time to rub some glycerin on it. Take a white piece of cloth and apply some glycerin on it before rubbing it on the stain. Make sure that you do this gently by rubbing it in circular strokes. Keep on doing this until the stain is completely removed.
When the stain goes away leave it and let it dry.