Xbox Text Tutorial
Step 1: Transfer your Xbox live profile to a compatible USB stick
Step 2: Plug your USB into your pc/laptop
Step 3: Open Horizon and inject map then select your profile
Step 4: When it saves, plug your USB back into your xbox
Step 5: (Optional) Move profile back to Hard Drive or keep on USB (Your choice)
Step 6: Start Minecraft, click play game then choose your USB after clicking play
Step 7: Enjoy the worlds, and remember ConsoleCrafted is the best source for map downloads!
Xbox 360 to Xbox One Transfer Text Tutorial
NOTE: Must complete all steps above to transfer a downloaded world, or you could just transfer a world you already have...
Step 8: On the Mincraft Xbox 360 menu, go to play game.
Step 9: (Must be online) hover over the map you want to transfer, and click "Y", then "Upload Save"
Step 10: Log onto your Xbox One and onto the Minecraft "Play Game" menu click "X" to retrieve save.
Step 11: YOUR DONE! ;)