ROM flashing tutorial reference: http://bbs.elephone.hk/thread-1037-1-1.html#.VXAbSfRAU-0
You can flash by USB cable no need for recovery. Please choose ” Firmware update” when flashing.
You’d better conduct factory reset and wipe cache partition first . Back up your phone before factory reset. If there are some errors during flashing, you can flash official rom first and then try again.