I purchased the premium version so that I would not be annoyed by the ads. Plus, it is a good app, so I am willing to pay the developers for their time.
However, I only have the full version in iTunes and installed on my iPhone. I really do not want to purchase something a second time that I have already purchased once. How do I get the premium version that I paid for?
All purchases are tied to your iTunes account. If you sign in with the same account you used to make your purchase you should be able to download from iTunes with no extra charge.