Some inventors specialize in making changes to products that already exist, in order to improve them. However, if you plan to alter an existing invention, make sure that you change the item enough to make it different from the original, and obtain patent protection on the product you are attempting to improve.
Perform your due diligence. Go to the web site of the U.S. Patent and Trademark Office to determine if a patent already exists on the product you want to improve. Keep in mind that not all inventions sold by entrepreneurs have registered patents.
Conduct market research. One simple way to get started is to go to big box retail stores in your local area and look at the products on sale. Determine if there are any items in these stores that are similar to the product you want to improve. Find out the number of sales the product has made, amount of revenue it has generated, other possible venues in which to market the product, and the number of stores that currently sell the invention.
Analyze the existing product. Determine what improvements you can perform to make the product more effective, generate more revenue, look differently, and/or save on manufacturing costs. Look at the amount of competition the product currently has from other companies, and decide if you are ready to face those challenges.
Hire a lawyer who specializes in patent protection. Ask him or her to give you an informed opinion on your chances of obtaining an "improvement patent" for your altered invention idea. Let the lawyer handle the entire process of obtaining a patent for this invention, which can include research on existing patents both in America and other countries. Also ask your attorney to make sure that your proposed product logo does not too closely resemble any existing ones.