To make genetic mutations you have to change DNA. RNA is generally "transcribed" or copied from the DNA template, which is like the master code. RNA is made in small pieces as needed, and there can be hundreds of times more RNA than DNA in a cell at any given time....but RNA is disposable and is degraded as soon as it is used. One way to think of this is that DNA is a textbook, RNA is a handout, and those handouts are used to get things done and then thrown out. If you change the handout, only a few people will be affected, but if you change the textbook then everyone will be affected forever.

Both are genetic mutations.In our cells, most RNA is copied from DNA and then eventually disposed of. DNA is generally permanent, so changes to DNA (mutations) also tend to be permanent. But sometimes a cell will notice a mutation and repair the DNA instead. Also, changes to some kinds of RNA can affect whether the cell obeys (transcribes) the original DNA instructions or not. So changes to both DNA and RNA can both be described as genetic mutations.

You would need to change DNA to make a permanent mutation. I'm guessing from your question that you sort of know how the DNA-RNA system works. Genes in DNA hold the code for making proteins; DNA is transcribed into RNA, which carries the code from the nucleus out into the cell, where the RNA is translated into an actual protein. Individual RNA molecules get destroyed very soon after they are translated into protein, so if you mutated a strand of RNA this would only result in a few proteins being made incorrectly. However, if you mutate the DNA, then you will permanently change the cell and it will always make RNA and proteins containing that mutation.

DNA - RNA is just the intermediary that goes between DNA and protein. You can make mutant proteins by changing RNA, but you won't change the genetic code.