I'm 99% sure that irfanview will be able to help you. It is a small, fast, freeware image viewer that you can use to open the file, and then save it again to any format you like.
Not only does Prezi allow you to create non-linear presentations, it also makes it easy to apply transition animations between your frames. Learn how to apply a fade-in transition to select items and entire frames in this tutorial
Select "Edit Path"…