Scroll down and tap System (or About Phone on some UI versions).
Tap Check for Updates . The device will contact ZTE’s servers. How to Update Software on ZTE Blade A35 Core
Download and install ZTE USB Driver and ZTE Firmware Upgrade Tool from the official ZTE support website. Scroll down and tap System (or About Phone
Power off the Blade A35 Core. Press and hold Volume Down while connecting to PC via USB. How to Update Software on ZTE Blade A35 Core