Hi Cindie,
The message you saw means that the version that's on your tablet is the newest one put out specifically for your table by RCA. I don't know what year your tablet was made, but generally manufacturers only continue to support Android updates for a certain amount of time once they stop making a particular model. It sounds like RCA hasn't made any more updates past the one you have, and I doubt at this point that they will. These are inexpensive tablets and I doubt they will justify any ongoing development efforts in the future, so don't expect any new updates either.
For Android experts, there are ways to update the operating system of your tablet, but it does require somewhat specialized knowledge of the software internals. You might try checking out [link|https://xdaforums.com/|XDA Forums|new_window=true] if you're interested in the subject.