How do I transfer minecraft worlds from my Xbox 360 to my Xbox One?

If you own both the 360 and One versions of Minecraft, that's all you need. The $4.99 was an upgrade that was available to people who owned the 360 version and wanted to upgrade to the Xbox One edition, but that promotion is over.

To transfer the world, you have to load it on the 360 and upload it to the cloud (there's a menu option in the game for it), and then on the Xbox One version you can download it from the cloud. If you have more than one world that you want to transfer then you have to do these steps multiple times. You can't just use a flash drive.