For all  OPPO smartphones

Note: Back up your data before doing an update. Although OTA Update doesn't require to back up your data, it still best to make backing up data a practice every time you update anything on your phone. Make it a habit at any time.

Plug your OPPO phone into power, or keep the battery level over 40%. 

Do not operate or power off your device during the process. 

FOR UPDATE OPPO SMARTPHONES:

 - Automatic OTA update

   1. - Connect to a working Wi-Fi or Mobile network. The system will automatically show new update if any.

   You can see a notification on the "System updates" icon, otherwise, it will show       "It is already the latest version".

   2.-  Download the firmware. Download under a Wi-Fi network to avoid the consumption of your mobile data.

   3. - Tap [System Updates]. Your device will reboot and start updating, which will take a few minutes.

- Manually OTA update.

   1.- Go to settings menu.

   2.- Scroll to the bottom of this screen, and select “About phone”

   3.- Select the “System updates” option.

   4.- Select the “Yes” option.

   5.- The device will check the battery charge level and may ask you to further charge.

 

- Other ways you can update the software of your device:

   Update Software with an SD Card (Recovery Update), (advanced mode)

      Important!! ...  Back up your data.

      Update with SD card is mainly used if the phone freezes at a certain interface or OPPO logo, or can't boot but can get into Recovery Mode.

      1.-  Go to OPPO Official Website > Click Support > Software Updates

      download the firmware to the root directory of your SD Card (A root directory is a top-most directory in the SD             

      Card file systems).

      2.-  Insert your SD card, then power off the phone.

      3.- Press and hold the Power and Volume Down buttons, until your phone enters Recovery Mode.

  

     4.-  Under the Recovery Mode, tap [Install from storage device] > [Install from SD], find the update package.

     5.-  Tap the firmware. A confirmation message will appear on your screen. Tap Yes.

     Your device will reboot and start updating, which will take some time.

 

SOURCE:  Official site https://oppo-in.custhelp.com/app/answers/detail/a_id/116/~/updating-the-latest-software%3F-made-easier-with-these-steps