If it is a mobile phone, delete the MC on the home page, and then you will be reminded to find "residual files". This is the file. Click "Don't delete for the time being" to save the archive.

If it is a computer, the path: game \minecraft\saves\ archive, take away the archive folder, download the new MC, and then put the archive in: new game \. Minecraft \ save.

If it is suppressed by the Internet, upload and archive it, and then log in with the old account after downloading it.