How to upgrade system?
Download the software build for your device on this page. Please back up your data before flashing your device.
Plug your phone into your computer and copy the downloaded .zip to your phone’s storage. If you’re using a Mac, you can install Android File Transfer Android File Transfer for this operation.
After the .zip file is copied to your phone, go to 'Settings' - 'system update', click the 'settings' icon on the top right corner, choose 'Local upgrade', find the .zip file and click on 'Install' to confirm.
The update takes about a minute (depending upon the file size), once done reboot your device to boot into the latest Oxygen OS.