I own the Harry Potter audiobooks through Itunes. I'd like to download them again in a more portable format - or convert. Any clues?

Years ago, I purchased the Harry Potter audiobooks (read by Jim Dale) through ITunes. These are sensational performances that are legendary in their own right.

But now I have a variety of devices, and Ipods (on which I listened) are no longer supported. I'd like to switch formats here, but am not entirely sure how to do it.