If the OTA says “Your system is up to date” and you are still on Android 6.0, Oppo may have stopped pushing updates. Proceed to Method 2.
The Oppo F3 and its variant, the Oppo F3 Plus, were officially updated from Android 6.0 to with Oppo’s ColorOS 3.0 interface. After that, Oppo shifted its development focus to newer devices like the Oppo F5, F7, and the Find series. Oppo F3 Update 8.0 Download