If it doesn't work the first time, I suggest closing the application and trying a couple more times. I had to do it six times before it finally worked.
It took me a couple of tries but it eventually worked. All my worlds were still there.
I have the disc version and I upgraded from Editions.
If it doesn't work the first time, I suggest closing the application and trying a couple more times. I had to do it six times before it finally worked.