David Irving, 67, pleaded guilty to making the remarks in a 1989 speech, but decided to file an appeal Wednesday after learning an Austrian prosecutor wanted to have his 3-year prison sentence lengthened.
In an interview with Sky News, Irving said he was now expressing different opinions because he had looked at more archive material since his speeches in 1989.
"But when you come to Auschwitz, which is the big tourist display they have now in Poland, I don't believe half of what they show you," he told Sky News. "Some of the buildings they show you were built after the war, as the Polish government admits.
"That's not denying the Holocaust ... I want to be told the truth and nothing but the truth."
He said every historian should be ready to refine their positions, but "a lot of them don't, particularly in Germany and Austria."