The word “disinterested" is generally used to mean that a person has no reason at all to support one side or another in a matter or dispute. This is because he or she has no personal advantage, financial or otherwise, from the win of either side. Perhaps he or she has something more necessary or interesting to do than to take part in the matter. It can be replaced by the synonym “disagreed". A “disinterested" person in a dispute is often “a neutral person".
The word “uninterested" is mostly used in a negative sense, meaning that the person is idle by nature. He has no curiosity or enthusiasm about anything, or a particular matter, simply because his lack of diligence.
1. Since I have no gain from either side, I can judge the dispute in a disinterested (= neutral) manner.
2. I was trying to teach Ram the basics of English grammar, but he was completely uninterested. Naturally, he could not learn anything.