The best way to remove dried fabric paint is to peel or scrape it off clothing with a dull knife. If that does not work, use a combination of water and detergent, alcohol or acetone.
Always begin with the most gentle removal method of peeling and scraping. If you do not see your desired results, soak a sponge with warm water, and pat the stain. Add dish detergent to the water, then rinse and repeat.
If water and detergent do not remove the stain, use a cotton ball to blot the paint with hairspray or nail polish remover. Alternatively, place a white cloth under the fabric, and blot the paint with rubbing alcohol.