I am using a Lenovo A6000 Android phone. My default file manager is other than ES File Manager.
How can I set the ES File manager as default and uninstall the in-built file manager?.
To uninstall, go to Settings -> Applications and select the app. You will have the option to uninstall. If it is part of the ROM, you should have the option to disable it.
If you want to set ES Explorer as the default, go to the existing app as above, scroll down and tap on 'clear defaults'. This will pop a dialog next time Android wants to decide which app to open. (Usually when you connect a USB device or open a file picker, etc.) then you can select ES as the default.