According to Living Space 360, to remove dried gloss paint you need to use a scraper in combination with paint strippers. If the paint is water-based, use methylated spirits. If the paint is oil-based, then use white spirit, paint thinner or turpentine solution.
If the paint is dried on a fabric, apply your paint thinner and rub the dried paint stain with a cloth. Dried oil-based paint is more difficult to remove and even these materials may not lift a dried oil-based paint stain, according to Living Space 360. They recommend trying to freeze the fabric and chip away at the paint, if all else fails.
If you are attempting to remove the dried paint from walls, use the same materials — but you will need to alter the method. According to Do it Yourself, you need a scraper or razor blade. Scrape as much paint off of the wall as possible before applying a paint stripper. The paint stripper needs to penetrate the dried paint before it is able to further break it down so that you may scrape off more with your blade or scraper.
When working with paint strippers, always work in a well-ventilated environment.