Latex paint is a type of emulsion paint -- the acrylic plastic binders are suspended in water, and when the water evaporates, they create a solid coating that clings to the surface and gradually cures to turn hard. If the paint is wet, you can wipe it off with a wet rag to remove it. But the curing process is irreversible; once it's complete, you may have to resort to mechanical means to remove dried latex or emulsion paint. Before you do that, though, try a solvent, such as alcohol or ammonia.
Solvents that Remove Dried Latex Paint
Alcohol is a well-known cleaning agent for dried latex paint. The solvents in commercial latex paint removers are various types of alcohols, but you can use isopropyl -- or rubbing -- alcohol as well as denatured alcohol from the paint store. You may also have luck removing dried paint stains from furniture and floors using a dilute solution of ammonia and water. Moreover, soap and water often help loosen the bond of the paint from the surface it's adhered to when you want to remove the paint.
Using a Solvent
Always test the solvent you're going to use on the substrate to which the paint adheres before using it, to make sure it won't damage the finish or the surface itself. This is particularly important if you're trying to remove paint from plastic. If the solvent is safe, you can proceed:
Apply the solvent liberally to the paint with a rag or a cotton swab.
Wait for the paint to soften. This may take some time, and may require more applications of solvent or cleaning agent.
Scrape as much of the softened paint away as possible. Use a plastic paint scraper if you're worried about damaging the surface to which the paint adheres. Otherwise, use a metal scraper or a razor blade.
Soak a rag with the solvent or cleaner and wipe away the residue after you've scraped off as much as you can.
Scraping With a Pull Scraper
If you can't use alcohol or latex paint remover for fear of damaging the finish of the item, and ammonia or soap don't seem to do the job, it's possible to scrape the bulk of the paint off with a pull scraper:
Hold the scraper on the edge of a paint spill that you can't soften with alcohol, and draw it toward you, using light pressure to remove a thin layer of paint.
Repeat this scraping technique, each time removing a thin layer of paint while ensuring the scraper doesn't come into the contact with the surface underneath.
Stop scraping when only a small film of residue remains. You should be able to wash off this film with a rag and soap and water.