Hi, here is the firmware of Ecoo E04 Plus 3GB. This firmware if for ECOO E04 Plus upgrade to Android 5.0 OS.
Firmware: ECOO E04 Plus 3GB MTK6752 Smartphone Upgrade to Android 5.0 Firmware
These are the Tutorial guides:
Tutorial for the whole process of flashing ROM
Firmware update by USB wire Tutorial
Tutorial and download for SPFT Driver installation
Have a nice day!