How to backup your Minecraft: Pocket Edition worlds?
On the PC:
Connect your mobile device to the PC via USB.
Pick your device from the available drives:
Go to Internal storage → Games → com.mojang → minecraftWorlds
Copy saved worlds and paste somewhere on the PC or to a cloud storage.
If for some reason you will lose your worlds, you can always access the backup folder and paste the games back to your mobile device.
Warning! Please do not remove any files from your device.
It is possible that you will not be able to access this file on your PC. If that happens - please try different method.
On your mobile device:
To access the files on your mobile device you will need an application from Play Store.
Some examples of apps that will let you browse your files:
Those apps are only a recommendation, if you have another application to browse your files - you can keep using it.
Go to the file explorer app of your choice.
Access folders: Storage → SDcard → games → com.mojang → minecraftWorlds.
Pick the worlds you wish to copy and paste them to a different location (preferably not in the games folder). Some of the file managers have an option to copy your files to cloud service but you can also do it manually, so you can always backup your worlds easily.