The method depends on whether it's wood or fabric furniture. Here's a link to a upholstered chair video done by a Hometalk member. It's a long video but you should learn a lot about what to do to have a successful project.
If it's wood, clean it well then lightly sand so the paint will adhere. Clean off the sanding dust then prime and paint it. I hope that helps. Wishing you the best.
Carol...You can use slip covers.
Carol: maybe these will help
Do you want to change fabric color?
Fabric or wood?
Depends if it's fabric or wood.
You can paint over any of it, but I personally don't recommend painting over fabric. Unless it's a quick fix until you can afford to recover it.
Painting over wood or already painted surface is simple as long as the finish is in good condition first.
Here is how to paint furniture. https://www.arayofsunlight.com/how-to-paint-furniture/
what type of furniture? Wood, cloth, leather?