These hand-held tools have a sturdy flat blade for scraping and cutting old paint from the surface to be repainted. They come in a variety of sizes, and some have other tools attached to them such as a stiff wire brush or a caulk-removal tool. Applying heat or a paint stripper before scraping can loosen the paint and make for easier removal. Most large hardware stores will carry a wide variety of paint scrapers.
Sand paper works well for finer finishes. The paper can be used in the palm of your hand, in a hand-held sanding block or pole, and attached to a powered sanding device. A hardware store will carry these items.
For removing a lot of loose paint from a large area quickly, a power washer with a hose is the way to go. It works by using an air compressor that ejects the water through a wand at a very high pressure and blasts the paint away. These can be gasoline or electric powered. You can purchase or rent these tools at hardware stores.