Under some circumstances, patent laws allow an inventor to patent a modification or upgrade to an existing device. But, there has to be a substantial upgrade. Typical example is the tale of an inventor named Gilmore. He came up with a modification to an existing carburetor for an aircraft engine. His patent request was turned down though by the patent office. They did not feel there was a substantial difference between the existing carburetor and his modified carburetor to justify a new patent.